doc.2021.01.06a: Documentation updates.
fixes.2021.01.04b: Miscellaneous fixes.
kfree_rcu.2021.01.04a: kfree_rcu() updates.
mmdumpobj.2021.01.22a: Dump allocation point for memory blocks.
nocb.2021.01.06a: RCU callback offload updates and cblist segment lengths.
rt.2021.01.04a: Real-time updates.
stall.2021.01.06a: RCU CPU stall warning updates.
torture.2021.01.12a: Torture-test updates and polling SRCU grace-period API.
tortureall.2021.01.06a: Torture-test script updates.
RCU-preempt Expedited Grace Periods
===================================
-``CONFIG_PREEMPT=y`` kernels implement RCU-preempt.
+``CONFIG_PREEMPTION=y`` kernels implement RCU-preempt.
The overall flow of the handling of a given CPU by an RCU-preempt
expedited grace period is shown in the following diagram:
RCU-sched Expedited Grace Periods
---------------------------------
-``CONFIG_PREEMPT=n`` kernels implement RCU-sched. The overall flow of
+``CONFIG_PREEMPTION=n`` kernels implement RCU-sched. The overall flow of
the handling of a given CPU by an RCU-sched expedited grace period is
shown in the following diagram:
RCU's grace-period guarantee allows updaters to wait for the completion
of all pre-existing RCU read-side critical sections. An RCU read-side
-critical section begins with the marker ``rcu_read_lock()`` and ends
-with the marker ``rcu_read_unlock()``. These markers may be nested, and
+critical section begins with the marker rcu_read_lock() and ends
+with the marker rcu_read_unlock(). These markers may be nested, and
RCU treats a nested set as one big RCU read-side critical section.
-Production-quality implementations of ``rcu_read_lock()`` and
-``rcu_read_unlock()`` are extremely lightweight, and in fact have
+Production-quality implementations of rcu_read_lock() and
+rcu_read_unlock() are extremely lightweight, and in fact have
exactly zero overhead in Linux kernels built for production use with
-``CONFIG_PREEMPT=n``.
+``CONFIG_PREEMPTION=n``.
This guarantee allows ordering to be enforced with extremely low
overhead to readers, for example:
15 WRITE_ONCE(y, 1);
16 }
-Because the ``synchronize_rcu()`` on line 14 waits for all pre-existing
-readers, any instance of ``thread0()`` that loads a value of zero from
-``x`` must complete before ``thread1()`` stores to ``y``, so that
+Because the synchronize_rcu() on line 14 waits for all pre-existing
+readers, any instance of thread0() that loads a value of zero from
+``x`` must complete before thread1() stores to ``y``, so that
instance must also load a value of zero from ``y``. Similarly, any
-instance of ``thread0()`` that loads a value of one from ``y`` must have
-started after the ``synchronize_rcu()`` started, and must therefore also
+instance of thread0() that loads a value of one from ``y`` must have
+started after the synchronize_rcu() started, and must therefore also
load a value of one from ``x``. Therefore, the outcome:
::
+-----------------------------------------------------------------------+
| Wait a minute! You said that updaters can make useful forward |
| progress concurrently with readers, but pre-existing readers will |
-| block ``synchronize_rcu()``!!! |
+| block synchronize_rcu()!!! |
| Just who are you trying to fool??? |
+-----------------------------------------------------------------------+
| **Answer**: |
+-----------------------------------------------------------------------+
| First, if updaters do not wish to be blocked by readers, they can use |
-| ``call_rcu()`` or ``kfree_rcu()``, which will be discussed later. |
-| Second, even when using ``synchronize_rcu()``, the other update-side |
+| call_rcu() or kfree_rcu(), which will be discussed later. |
+| Second, even when using synchronize_rcu(), the other update-side |
| code does run concurrently with readers, whether pre-existing or not. |
+-----------------------------------------------------------------------+
29 WRITE_ONCE(state, STATE_NORMAL);
30 }
-The RCU read-side critical section in ``do_something_dlm()`` works with
-the ``synchronize_rcu()`` in ``start_recovery()`` to guarantee that
-``do_something()`` never runs concurrently with ``recovery()``, but with
-little or no synchronization overhead in ``do_something_dlm()``.
+The RCU read-side critical section in do_something_dlm() works with
+the synchronize_rcu() in start_recovery() to guarantee that
+do_something() never runs concurrently with recovery(), but with
+little or no synchronization overhead in do_something_dlm().
+-----------------------------------------------------------------------+
| **Quick Quiz**: |
+-----------------------------------------------------------------------+
-| Why is the ``synchronize_rcu()`` on line 28 needed? |
+| Why is the synchronize_rcu() on line 28 needed? |
+-----------------------------------------------------------------------+
| **Answer**: |
+-----------------------------------------------------------------------+
| Without that extra grace period, memory reordering could result in |
-| ``do_something_dlm()`` executing ``do_something()`` concurrently with |
-| the last bits of ``recovery()``. |
+| do_something_dlm() executing do_something() concurrently with |
+| the last bits of recovery(). |
+-----------------------------------------------------------------------+
In order to avoid fatal problems such as deadlocks, an RCU read-side
-critical section must not contain calls to ``synchronize_rcu()``.
+critical section must not contain calls to synchronize_rcu().
Similarly, an RCU read-side critical section must not contain anything
that waits, directly or indirectly, on completion of an invocation of
-``synchronize_rcu()``.
+synchronize_rcu().
Although RCU's grace-period guarantee is useful in and of itself, with
`quite a few use cases <https://lwn.net/Articles/573497/>`__, it would
be good to be able to use RCU to coordinate read-side access to linked
data structures. For this, the grace-period guarantee is not sufficient,
-as can be seen in function ``add_gp_buggy()`` below. We will look at the
+as can be seen in function add_gp_buggy() below. We will look at the
reader's code later, but in the meantime, just think of the reader as
locklessly picking up the ``gp`` pointer, and, if the value loaded is
non-\ ``NULL``, locklessly accessing the ``->a`` and ``->b`` fields.
RCU's publish-subscribe guarantee allows data to be inserted into a
linked data structure without disrupting RCU readers. The updater uses
-``rcu_assign_pointer()`` to insert the new data, and readers use
-``rcu_dereference()`` to access data, whether new or old. The following
+rcu_assign_pointer() to insert the new data, and readers use
+rcu_dereference() to access data, whether new or old. The following
shows an example of insertion:
::
15 return true;
16 }
-The ``rcu_assign_pointer()`` on line 13 is conceptually equivalent to a
+The rcu_assign_pointer() on line 13 is conceptually equivalent to a
simple assignment statement, but also guarantees that its assignment
will happen after the two assignments in lines 11 and 12, similar to the
C11 ``memory_order_release`` store operation. It also prevents any
+-----------------------------------------------------------------------+
| **Quick Quiz**: |
+-----------------------------------------------------------------------+
-| But ``rcu_assign_pointer()`` does nothing to prevent the two |
+| But rcu_assign_pointer() does nothing to prevent the two |
| assignments to ``p->a`` and ``p->b`` from being reordered. Can't that |
| also cause problems? |
+-----------------------------------------------------------------------+
It is tempting to assume that the reader need not do anything special to
control its accesses to the RCU-protected data, as shown in
-``do_something_gp_buggy()`` below:
+do_something_gp_buggy() below:
::
12 }
However, this temptation must be resisted because there are a
-surprisingly large number of ways that the compiler (to say nothing of
-`DEC Alpha CPUs <https://h71000.www7.hp.com/wizard/wiz_2637.html>`__)
-can trip this code up. For but one example, if the compiler were short
-of registers, it might choose to refetch from ``gp`` rather than keeping
-a separate copy in ``p`` as follows:
+surprisingly large number of ways that the compiler (or weak ordering
+CPUs like the DEC Alpha) can trip this code up. For but one example, if
+the compiler were short of registers, it might choose to refetch from
+``gp`` rather than keeping a separate copy in ``p`` as follows:
::
the current structure with a new one, the fetches of ``gp->a`` and
``gp->b`` might well come from two different structures, which could
cause serious confusion. To prevent this (and much else besides),
-``do_something_gp()`` uses ``rcu_dereference()`` to fetch from ``gp``:
+do_something_gp() uses rcu_dereference() to fetch from ``gp``:
::
11 return false;
12 }
-The ``rcu_dereference()`` uses volatile casts and (for DEC Alpha) memory
+The rcu_dereference() uses volatile casts and (for DEC Alpha) memory
barriers in the Linux kernel. Should a `high-quality implementation of
C11 ``memory_order_consume``
[PDF] <http://www.rdrop.com/users/paulmck/RCU/consume.2015.07.13a.pdf>`__
-ever appear, then ``rcu_dereference()`` could be implemented as a
+ever appear, then rcu_dereference() could be implemented as a
``memory_order_consume`` load. Regardless of the exact implementation, a
-pointer fetched by ``rcu_dereference()`` may not be used outside of the
+pointer fetched by rcu_dereference() may not be used outside of the
outermost RCU read-side critical section containing that
-``rcu_dereference()``, unless protection of the corresponding data
+rcu_dereference(), unless protection of the corresponding data
element has been passed from RCU to some other synchronization
mechanism, most commonly locking or `reference
counting <https://www.kernel.org/doc/Documentation/RCU/rcuref.txt>`__.
-In short, updaters use ``rcu_assign_pointer()`` and readers use
-``rcu_dereference()``, and these two RCU API elements work together to
+In short, updaters use rcu_assign_pointer() and readers use
+rcu_dereference(), and these two RCU API elements work together to
ensure that readers have a consistent view of newly added data elements.
Of course, it is also necessary to remove elements from RCU-protected
the newly removed data element).
#. At this point, only the updater has a reference to the newly removed
data element, so it can safely reclaim the data element, for example,
- by passing it to ``kfree()``.
+ by passing it to kfree().
-This process is implemented by ``remove_gp_synchronous()``:
+This process is implemented by remove_gp_synchronous():
::
This function is straightforward, with line 13 waiting for a grace
period before line 14 frees the old data element. This waiting ensures
-that readers will reach line 7 of ``do_something_gp()`` before the data
-element referenced by ``p`` is freed. The ``rcu_access_pointer()`` on
-line 6 is similar to ``rcu_dereference()``, except that:
+that readers will reach line 7 of do_something_gp() before the data
+element referenced by ``p`` is freed. The rcu_access_pointer() on
+line 6 is similar to rcu_dereference(), except that:
-#. The value returned by ``rcu_access_pointer()`` cannot be
+#. The value returned by rcu_access_pointer() cannot be
dereferenced. If you want to access the value pointed to as well as
- the pointer itself, use ``rcu_dereference()`` instead of
- ``rcu_access_pointer()``.
-#. The call to ``rcu_access_pointer()`` need not be protected. In
- contrast, ``rcu_dereference()`` must either be within an RCU
+ the pointer itself, use rcu_dereference() instead of
+ rcu_access_pointer().
+#. The call to rcu_access_pointer() need not be protected. In
+ contrast, rcu_dereference() must either be within an RCU
read-side critical section or in a code segment where the pointer
cannot change, for example, in code protected by the corresponding
update-side lock.
+-----------------------------------------------------------------------+
| **Quick Quiz**: |
+-----------------------------------------------------------------------+
-| Without the ``rcu_dereference()`` or the ``rcu_access_pointer()``, |
+| Without the rcu_dereference() or the rcu_access_pointer(), |
| what destructive optimizations might the compiler make use of? |
+-----------------------------------------------------------------------+
| **Answer**: |
+-----------------------------------------------------------------------+
-| Let's start with what happens to ``do_something_gp()`` if it fails to |
-| use ``rcu_dereference()``. It could reuse a value formerly fetched |
+| Let's start with what happens to do_something_gp() if it fails to |
+| use rcu_dereference(). It could reuse a value formerly fetched |
| from this same pointer. It could also fetch the pointer from ``gp`` |
| in a byte-at-a-time manner, resulting in *load tearing*, in turn |
| resulting a bytewise mash-up of two distinct pointer values. It might |
| update has changed the pointer to match the wrong guess. Too bad |
| about any dereferences that returned pre-initialization garbage in |
| the meantime! |
-| For ``remove_gp_synchronous()``, as long as all modifications to |
+| For remove_gp_synchronous(), as long as all modifications to |
| ``gp`` are carried out while holding ``gp_lock``, the above |
| optimizations are harmless. However, ``sparse`` will complain if you |
| define ``gp`` with ``__rcu`` and then access it without using either |
-| ``rcu_access_pointer()`` or ``rcu_dereference()``. |
+| rcu_access_pointer() or rcu_dereference(). |
+-----------------------------------------------------------------------+
In short, RCU's publish-subscribe guarantee is provided by the
-combination of ``rcu_assign_pointer()`` and ``rcu_dereference()``. This
+combination of rcu_assign_pointer() and rcu_dereference(). This
guarantee allows data elements to be safely added to RCU-protected
linked data structures without disrupting RCU readers. This guarantee
can be used in combination with the grace-period guarantee to also allow
This guarantee was only partially premeditated. DYNIX/ptx used an
explicit memory barrier for publication, but had nothing resembling
-``rcu_dereference()`` for subscription, nor did it have anything
+rcu_dereference() for subscription, nor did it have anything
resembling the dependency-ordering barrier that was later subsumed
-into ``rcu_dereference()`` and later still into ``READ_ONCE()``. The
+into rcu_dereference() and later still into READ_ONCE(). The
need for these operations made itself known quite suddenly at a
late-1990s meeting with the DEC Alpha architects, back in the days when
DEC was still a free-standing company. It took the Alpha architects a
and C++ standards committees have provided much education on tricks and
traps from the compiler. In short, compilers were much less tricky in
the early 1990s, but in 2015, don't even think about omitting
-``rcu_dereference()``!
+rcu_dereference()!
Memory-Barrier Guarantees
~~~~~~~~~~~~~~~~~~~~~~~~~
systems with more than one CPU:
#. Each CPU that has an RCU read-side critical section that begins
- before ``synchronize_rcu()`` starts is guaranteed to execute a full
+ before synchronize_rcu() starts is guaranteed to execute a full
memory barrier between the time that the RCU read-side critical
- section ends and the time that ``synchronize_rcu()`` returns. Without
+ section ends and the time that synchronize_rcu() returns. Without
this guarantee, a pre-existing RCU read-side critical section might
hold a reference to the newly removed ``struct foo`` after the
- ``kfree()`` on line 14 of ``remove_gp_synchronous()``.
+ kfree() on line 14 of remove_gp_synchronous().
#. Each CPU that has an RCU read-side critical section that ends after
- ``synchronize_rcu()`` returns is guaranteed to execute a full memory
- barrier between the time that ``synchronize_rcu()`` begins and the
+ synchronize_rcu() returns is guaranteed to execute a full memory
+ barrier between the time that synchronize_rcu() begins and the
time that the RCU read-side critical section begins. Without this
guarantee, a later RCU read-side critical section running after the
- ``kfree()`` on line 14 of ``remove_gp_synchronous()`` might later run
- ``do_something_gp()`` and find the newly deleted ``struct foo``.
-#. If the task invoking ``synchronize_rcu()`` remains on a given CPU,
+ kfree() on line 14 of remove_gp_synchronous() might later run
+ do_something_gp() and find the newly deleted ``struct foo``.
+#. If the task invoking synchronize_rcu() remains on a given CPU,
then that CPU is guaranteed to execute a full memory barrier sometime
- during the execution of ``synchronize_rcu()``. This guarantee ensures
- that the ``kfree()`` on line 14 of ``remove_gp_synchronous()`` really
+ during the execution of synchronize_rcu(). This guarantee ensures
+ that the kfree() on line 14 of remove_gp_synchronous() really
does execute after the removal on line 11.
-#. If the task invoking ``synchronize_rcu()`` migrates among a group of
+#. If the task invoking synchronize_rcu() migrates among a group of
CPUs during that invocation, then each of the CPUs in that group is
guaranteed to execute a full memory barrier sometime during the
- execution of ``synchronize_rcu()``. This guarantee also ensures that
- the ``kfree()`` on line 14 of ``remove_gp_synchronous()`` really does
+ execution of synchronize_rcu(). This guarantee also ensures that
+ the kfree() on line 14 of remove_gp_synchronous() really does
execute after the removal on line 11, but also in the case where the
- thread executing the ``synchronize_rcu()`` migrates in the meantime.
+ thread executing the synchronize_rcu() migrates in the meantime.
+-----------------------------------------------------------------------+
| **Quick Quiz**: |
| Given that multiple CPUs can start RCU read-side critical sections at |
| any time without any ordering whatsoever, how can RCU possibly tell |
| whether or not a given RCU read-side critical section starts before a |
-| given instance of ``synchronize_rcu()``? |
+| given instance of synchronize_rcu()? |
+-----------------------------------------------------------------------+
| **Answer**: |
+-----------------------------------------------------------------------+
| If RCU cannot tell whether or not a given RCU read-side critical |
-| section starts before a given instance of ``synchronize_rcu()``, then |
+| section starts before a given instance of synchronize_rcu(), then |
| it must assume that the RCU read-side critical section started first. |
-| In other words, a given instance of ``synchronize_rcu()`` can avoid |
+| In other words, a given instance of synchronize_rcu() can avoid |
| waiting on a given RCU read-side critical section only if it can |
-| prove that ``synchronize_rcu()`` started first. |
-| A related question is “When ``rcu_read_lock()`` doesn't generate any |
+| prove that synchronize_rcu() started first. |
+| A related question is “When rcu_read_lock() doesn't generate any |
| code, why does it matter how it relates to a grace period?” The |
-| answer is that it is not the relationship of ``rcu_read_lock()`` |
+| answer is that it is not the relationship of rcu_read_lock() |
| itself that is important, but rather the relationship of the code |
| within the enclosed RCU read-side critical section to the code |
| preceding and following the grace period. If we take this viewpoint, |
| Yes, they really are required. To see why the first guarantee is |
| required, consider the following sequence of events: |
| |
-| #. CPU 1: ``rcu_read_lock()`` |
+| #. CPU 1: rcu_read_lock() |
| #. CPU 1: ``q = rcu_dereference(gp); /* Very likely to return p. */`` |
| #. CPU 0: ``list_del_rcu(p);`` |
-| #. CPU 0: ``synchronize_rcu()`` starts. |
+| #. CPU 0: synchronize_rcu() starts. |
| #. CPU 1: ``do_something_with(q->a);`` |
| ``/* No smp_mb(), so might happen after kfree(). */`` |
-| #. CPU 1: ``rcu_read_unlock()`` |
-| #. CPU 0: ``synchronize_rcu()`` returns. |
+| #. CPU 1: rcu_read_unlock() |
+| #. CPU 0: synchronize_rcu() returns. |
| #. CPU 0: ``kfree(p);`` |
| |
| Therefore, there absolutely must be a full memory barrier between the |
| is roughly similar: |
| |
| #. CPU 0: ``list_del_rcu(p);`` |
-| #. CPU 0: ``synchronize_rcu()`` starts. |
-| #. CPU 1: ``rcu_read_lock()`` |
+| #. CPU 0: synchronize_rcu() starts. |
+| #. CPU 1: rcu_read_lock() |
| #. CPU 1: ``q = rcu_dereference(gp);`` |
| ``/* Might return p if no memory barrier. */`` |
-| #. CPU 0: ``synchronize_rcu()`` returns. |
+| #. CPU 0: synchronize_rcu() returns. |
| #. CPU 0: ``kfree(p);`` |
| #. CPU 1: ``do_something_with(q->a); /* Boom!!! */`` |
-| #. CPU 1: ``rcu_read_unlock()`` |
+| #. CPU 1: rcu_read_unlock() |
| |
| And similarly, without a memory barrier between the beginning of the |
| grace period and the beginning of the RCU read-side critical section, |
+-----------------------------------------------------------------------+
| **Quick Quiz**: |
+-----------------------------------------------------------------------+
-| You claim that ``rcu_read_lock()`` and ``rcu_read_unlock()`` generate |
+| You claim that rcu_read_lock() and rcu_read_unlock() generate |
| absolutely no code in some kernel builds. This means that the |
| compiler might arbitrarily rearrange consecutive RCU read-side |
| critical sections. Given such rearrangement, if a given RCU read-side |
+-----------------------------------------------------------------------+
| **Answer**: |
+-----------------------------------------------------------------------+
-| In cases where ``rcu_read_lock()`` and ``rcu_read_unlock()`` generate |
+| In cases where rcu_read_lock() and rcu_read_unlock() generate |
| absolutely no code, RCU infers quiescent states only at special |
| locations, for example, within the scheduler. Because calls to |
-| ``schedule()`` had better prevent calling-code accesses to shared |
-| variables from being rearranged across the call to ``schedule()``, if |
+| schedule() had better prevent calling-code accesses to shared |
+| variables from being rearranged across the call to schedule(), if |
| RCU detects the end of a given RCU read-side critical section, it |
| will necessarily detect the end of all prior RCU read-side critical |
| sections, no matter how aggressively the compiler scrambles the code. |
then might acquire the update-side spinlock in order to update that
element, all while remaining in that RCU read-side critical section. Of
course, it is necessary to exit the RCU read-side critical section
-before invoking ``synchronize_rcu()``, however, this inconvenience can
-be avoided through use of the ``call_rcu()`` and ``kfree_rcu()`` API
+before invoking synchronize_rcu(), however, this inconvenience can
+be avoided through use of the call_rcu() and kfree_rcu() API
members described later in this document.
+-----------------------------------------------------------------------+
Readers Impose Minimal Ordering
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Reader-side markers such as ``rcu_read_lock()`` and
-``rcu_read_unlock()`` provide absolutely no ordering guarantees except
+Reader-side markers such as rcu_read_lock() and
+rcu_read_unlock() provide absolutely no ordering guarantees except
through their interaction with the grace-period APIs such as
-``synchronize_rcu()``. To see this, consider the following pair of
+synchronize_rcu(). To see this, consider the following pair of
threads:
::
18 rcu_read_unlock();
19 }
-After ``thread0()`` and ``thread1()`` execute concurrently, it is quite
+After thread0() and thread1() execute concurrently, it is quite
possible to have
::
(r1 == 1 && r2 == 0)
(that is, ``y`` appears to have been assigned before ``x``), which would
-not be possible if ``rcu_read_lock()`` and ``rcu_read_unlock()`` had
+not be possible if rcu_read_lock() and rcu_read_unlock() had
much in the way of ordering properties. But they do not, so the CPU is
within its rights to do significant reordering. This is by design: Any
significant ordering constraints would slow down these fast-path APIs.
+-----------------------------------------------------------------------+
| **Answer**: |
+-----------------------------------------------------------------------+
-| No, the volatile casts in ``READ_ONCE()`` and ``WRITE_ONCE()`` |
+| No, the volatile casts in READ_ONCE() and WRITE_ONCE() |
| prevent the compiler from reordering in this particular case. |
+-----------------------------------------------------------------------+
Readers Do Not Exclude Updaters
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Neither ``rcu_read_lock()`` nor ``rcu_read_unlock()`` exclude updates.
+Neither rcu_read_lock() nor rcu_read_unlock() exclude updates.
All they do is to prevent grace periods from ending. The following
example illustrates this:
18 spin_unlock(&my_lock);
19 }
-If the ``thread0()`` function's ``rcu_read_lock()`` excluded the
-``thread1()`` function's update, the ``WARN_ON()`` could never fire. But
-the fact is that ``rcu_read_lock()`` does not exclude much of anything
-aside from subsequent grace periods, of which ``thread1()`` has none, so
-the ``WARN_ON()`` can and does fire.
+If the thread0() function's rcu_read_lock() excluded the
+thread1() function's update, the WARN_ON() could never fire. But
+the fact is that rcu_read_lock() does not exclude much of anything
+aside from subsequent grace periods, of which thread1() has none, so
+the WARN_ON() can and does fire.
Updaters Only Wait For Old Readers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-It might be tempting to assume that after ``synchronize_rcu()``
+It might be tempting to assume that after synchronize_rcu()
completes, there are no readers executing. This temptation must be
avoided because new readers can start immediately after
-``synchronize_rcu()`` starts, and ``synchronize_rcu()`` is under no
+synchronize_rcu() starts, and synchronize_rcu() is under no
obligation to wait for these new readers.
+-----------------------------------------------------------------------+
+-----------------------------------------------------------------------+
| **Answer**: |
+-----------------------------------------------------------------------+
-| For no time at all. Even if ``synchronize_rcu()`` were to wait until |
+| For no time at all. Even if synchronize_rcu() were to wait until |
| all readers had completed, a new reader might start immediately after |
-| ``synchronize_rcu()`` completed. Therefore, the code following |
-| ``synchronize_rcu()`` can *never* rely on there being no readers. |
+| synchronize_rcu() completed. Therefore, the code following |
+| synchronize_rcu() can *never* rely on there being no readers. |
+-----------------------------------------------------------------------+
Grace Periods Don't Partition Read-Side Critical Sections
28 rcu_read_unlock();
29 }
-Here, if ``(r1 == 1)``, then ``thread0()``'s write to ``b`` must happen
-before the end of ``thread1()``'s grace period. If in addition
-``(r4 == 1)``, then ``thread3()``'s read from ``b`` must happen after
-the beginning of ``thread2()``'s grace period. If it is also the case
-that ``(r2 == 1)``, then the end of ``thread1()``'s grace period must
-precede the beginning of ``thread2()``'s grace period. This mean that
+Here, if ``(r1 == 1)``, then thread0()'s write to ``b`` must happen
+before the end of thread1()'s grace period. If in addition
+``(r4 == 1)``, then thread3()'s read from ``b`` must happen after
+the beginning of thread2()'s grace period. If it is also the case
+that ``(r2 == 1)``, then the end of thread1()'s grace period must
+precede the beginning of thread2()'s grace period. This mean that
the two RCU read-side critical sections cannot overlap, guaranteeing
that ``(r3 == 1)``. As a result, the outcome:
b. Wait-free read-side primitives for real-time use.
This focus on read-mostly situations means that RCU must interoperate
-with other synchronization primitives. For example, the ``add_gp()`` and
-``remove_gp_synchronous()`` examples discussed earlier use RCU to
+with other synchronization primitives. For example, the add_gp() and
+remove_gp_synchronous() examples discussed earlier use RCU to
protect readers and locking to coordinate updaters. However, the need
extends much farther, requiring that a variety of synchronization
primitives be legal within RCU read-side critical sections, including
| sections. |
| Note that it *is* legal for a normal RCU read-side critical section |
| to conditionally acquire a sleeping locks (as in |
-| ``mutex_trylock()``), but only as long as it does not loop |
+| mutex_trylock()), but only as long as it does not loop |
| indefinitely attempting to conditionally acquire that sleeping locks. |
-| The key point is that things like ``mutex_trylock()`` either return |
+| The key point is that things like mutex_trylock() either return |
| with the mutex held, or return an error indication if the mutex was |
-| not immediately available. Either way, ``mutex_trylock()`` returns |
+| not immediately available. Either way, mutex_trylock() returns |
| immediately without sleeping. |
+-----------------------------------------------------------------------+
costs have plummeted. However, as I learned from Matt Mackall's
`bloatwatch <http://elinux.org/Linux_Tiny-FAQ>`__ efforts, memory
footprint is critically important on single-CPU systems with
-non-preemptible (``CONFIG_PREEMPT=n``) kernels, and thus `tiny
-RCU <https://lkml.kernel.org/g/20090113221724.GA15307@linux.vnet.ibm.com>`__
+non-preemptible (``CONFIG_PREEMPTION=n``) kernels, and thus `tiny
+RCU <https://lore.kernel.org/r/20090113221724.GA15307@linux.vnet.ibm.com>`__
was born. Josh Triplett has since taken over the small-memory banner
with his `Linux kernel tinification <https://tiny.wiki.kernel.org/>`__
project, which resulted in `SRCU <#Sleepable%20RCU>`__ becoming optional
The remaining performance requirements are, for the most part,
unsurprising. For example, in keeping with RCU's read-side
-specialization, ``rcu_dereference()`` should have negligible overhead
+specialization, rcu_dereference() should have negligible overhead
(for example, suppression of a few minor compiler optimizations).
-Similarly, in non-preemptible environments, ``rcu_read_lock()`` and
-``rcu_read_unlock()`` should have exactly zero overhead.
+Similarly, in non-preemptible environments, rcu_read_lock() and
+rcu_read_unlock() should have exactly zero overhead.
In preemptible environments, in the case where the RCU read-side
critical section was not preempted (as will be the case for the
-highest-priority real-time process), ``rcu_read_lock()`` and
-``rcu_read_unlock()`` should have minimal overhead. In particular, they
+highest-priority real-time process), rcu_read_lock() and
+rcu_read_unlock() should have minimal overhead. In particular, they
should not contain atomic read-modify-write operations, memory-barrier
instructions, preemption disabling, interrupt disabling, or backwards
branches. However, in the case where the RCU read-side critical section
-was preempted, ``rcu_read_unlock()`` may acquire spinlocks and disable
+was preempted, rcu_read_unlock() may acquire spinlocks and disable
interrupts. This is why it is better to nest an RCU read-side critical
section within a preempt-disable region than vice versa, at least in
cases where that critical section is short enough to avoid unduly
degrading real-time latencies.
-The ``synchronize_rcu()`` grace-period-wait primitive is optimized for
+The synchronize_rcu() grace-period-wait primitive is optimized for
throughput. It may therefore incur several milliseconds of latency in
addition to the duration of the longest RCU read-side critical section.
On the other hand, multiple concurrent invocations of
-``synchronize_rcu()`` are required to use batching optimizations so that
+synchronize_rcu() are required to use batching optimizations so that
they can be satisfied by a single underlying grace-period-wait
operation. For example, in the Linux kernel, it is not unusual for a
single grace-period-wait operation to serve more than `1,000 separate
invocations <https://www.usenix.org/conference/2004-usenix-annual-technical-conference/making-rcu-safe-deep-sub-millisecond-response>`__
-of ``synchronize_rcu()``, thus amortizing the per-invocation overhead
+of synchronize_rcu(), thus amortizing the per-invocation overhead
down to nearly zero. However, the grace-period optimization is also
required to avoid measurable degradation of real-time scheduling and
interrupt latencies.
-In some cases, the multi-millisecond ``synchronize_rcu()`` latencies are
-unacceptable. In these cases, ``synchronize_rcu_expedited()`` may be
+In some cases, the multi-millisecond synchronize_rcu() latencies are
+unacceptable. In these cases, synchronize_rcu_expedited() may be
used instead, reducing the grace-period latency down to a few tens of
microseconds on small systems, at least in cases where the RCU read-side
critical sections are short. There are currently no special latency
-requirements for ``synchronize_rcu_expedited()`` on large systems, but,
+requirements for synchronize_rcu_expedited() on large systems, but,
consistent with the empirical nature of the RCU specification, that is
subject to change. However, there most definitely are scalability
-requirements: A storm of ``synchronize_rcu_expedited()`` invocations on
+requirements: A storm of synchronize_rcu_expedited() invocations on
4096 CPUs should at least make reasonable forward progress. In return
-for its shorter latencies, ``synchronize_rcu_expedited()`` is permitted
+for its shorter latencies, synchronize_rcu_expedited() is permitted
to impose modest degradation of real-time latency on non-idle online
CPUs. Here, “modest” means roughly the same latency degradation as a
scheduling-clock interrupt.
There are a number of situations where even
-``synchronize_rcu_expedited()``'s reduced grace-period latency is
-unacceptable. In these situations, the asynchronous ``call_rcu()`` can
-be used in place of ``synchronize_rcu()`` as follows:
+synchronize_rcu_expedited()'s reduced grace-period latency is
+unacceptable. In these situations, the asynchronous call_rcu() can
+be used in place of synchronize_rcu() as follows:
::
28 }
A definition of ``struct foo`` is finally needed, and appears on
-lines 1-5. The function ``remove_gp_cb()`` is passed to ``call_rcu()``
+lines 1-5. The function remove_gp_cb() is passed to call_rcu()
on line 25, and will be invoked after the end of a subsequent grace
-period. This gets the same effect as ``remove_gp_synchronous()``, but
+period. This gets the same effect as remove_gp_synchronous(), but
without forcing the updater to wait for a grace period to elapse. The
-``call_rcu()`` function may be used in a number of situations where
-neither ``synchronize_rcu()`` nor ``synchronize_rcu_expedited()`` would
-be legal, including within preempt-disable code, ``local_bh_disable()``
+call_rcu() function may be used in a number of situations where
+neither synchronize_rcu() nor synchronize_rcu_expedited() would
+be legal, including within preempt-disable code, local_bh_disable()
code, interrupt-disable code, and interrupt handlers. However, even
-``call_rcu()`` is illegal within NMI handlers and from idle and offline
-CPUs. The callback function (``remove_gp_cb()`` in this case) will be
+call_rcu() is illegal within NMI handlers and from idle and offline
+CPUs. The callback function (remove_gp_cb() in this case) will be
executed within softirq (software interrupt) environment within the
Linux kernel, either within a real softirq handler or under the
-protection of ``local_bh_disable()``. In both the Linux kernel and in
+protection of local_bh_disable(). In both the Linux kernel and in
userspace, it is bad practice to write an RCU callback function that
takes too long. Long-running operations should be relegated to separate
threads or (in the Linux kernel) workqueues.
+-----------------------------------------------------------------------+
| **Quick Quiz**: |
+-----------------------------------------------------------------------+
-| Why does line 19 use ``rcu_access_pointer()``? After all, |
-| ``call_rcu()`` on line 25 stores into the structure, which would |
+| Why does line 19 use rcu_access_pointer()? After all, |
+| call_rcu() on line 25 stores into the structure, which would |
| interact badly with concurrent insertions. Doesn't this mean that |
-| ``rcu_dereference()`` is required? |
+| rcu_dereference() is required? |
+-----------------------------------------------------------------------+
| **Answer**: |
+-----------------------------------------------------------------------+
| Presumably the ``->gp_lock`` acquired on line 18 excludes any |
-| changes, including any insertions that ``rcu_dereference()`` would |
+| changes, including any insertions that rcu_dereference() would |
| protect against. Therefore, any insertions will be delayed until |
| after ``->gp_lock`` is released on line 25, which in turn means that |
-| ``rcu_access_pointer()`` suffices. |
+| rcu_access_pointer() suffices. |
+-----------------------------------------------------------------------+
-However, all that ``remove_gp_cb()`` is doing is invoking ``kfree()`` on
+However, all that remove_gp_cb() is doing is invoking kfree() on
the data element. This is a common idiom, and is supported by
-``kfree_rcu()``, which allows “fire and forget” operation as shown
+kfree_rcu(), which allows “fire and forget” operation as shown
below:
::
20 return true;
21 }
-Note that ``remove_gp_faf()`` simply invokes ``kfree_rcu()`` and
+Note that remove_gp_faf() simply invokes kfree_rcu() and
proceeds, without any need to pay any further attention to the
-subsequent grace period and ``kfree()``. It is permissible to invoke
-``kfree_rcu()`` from the same environments as for ``call_rcu()``.
-Interestingly enough, DYNIX/ptx had the equivalents of ``call_rcu()``
-and ``kfree_rcu()``, but not ``synchronize_rcu()``. This was due to the
+subsequent grace period and kfree(). It is permissible to invoke
+kfree_rcu() from the same environments as for call_rcu().
+Interestingly enough, DYNIX/ptx had the equivalents of call_rcu()
+and kfree_rcu(), but not synchronize_rcu(). This was due to the
fact that RCU was not heavily used within DYNIX/ptx, so the very few
-places that needed something like ``synchronize_rcu()`` simply
+places that needed something like synchronize_rcu() simply
open-coded it.
+-----------------------------------------------------------------------+
| **Quick Quiz**: |
+-----------------------------------------------------------------------+
-| Earlier it was claimed that ``call_rcu()`` and ``kfree_rcu()`` |
+| Earlier it was claimed that call_rcu() and kfree_rcu() |
| allowed updaters to avoid being blocked by readers. But how can that |
| be correct, given that the invocation of the callback and the freeing |
| of the memory (respectively) must still wait for a grace period to |
| definition would say that updates in garbage-collected languages |
| cannot complete until the next time the garbage collector runs, which |
| does not seem at all reasonable. The key point is that in most cases, |
-| an updater using either ``call_rcu()`` or ``kfree_rcu()`` can proceed |
-| to the next update as soon as it has invoked ``call_rcu()`` or |
-| ``kfree_rcu()``, without having to wait for a subsequent grace |
+| an updater using either call_rcu() or kfree_rcu() can proceed |
+| to the next update as soon as it has invoked call_rcu() or |
+| kfree_rcu(), without having to wait for a subsequent grace |
| period. |
+-----------------------------------------------------------------------+
But what if the updater must wait for the completion of code to be
executed after the end of the grace period, but has other tasks that can
be carried out in the meantime? The polling-style
-``get_state_synchronize_rcu()`` and ``cond_synchronize_rcu()`` functions
+get_state_synchronize_rcu() and cond_synchronize_rcu() functions
may be used for this purpose, as shown below:
::
18 return true;
19 }
-On line 14, ``get_state_synchronize_rcu()`` obtains a “cookie” from RCU,
+On line 14, get_state_synchronize_rcu() obtains a “cookie” from RCU,
then line 15 carries out other tasks, and finally, line 16 returns
immediately if a grace period has elapsed in the meantime, but otherwise
waits as required. The need for ``get_state_synchronize_rcu`` and
-``cond_synchronize_rcu()`` has appeared quite recently, so it is too
+cond_synchronize_rcu() has appeared quite recently, so it is too
early to tell whether they will stand the test of time.
RCU thus provides a range of tools to allow updaters to strike the
definition prevent later grace periods from ever completing. For a more
involved example, consider a 64-CPU system built with
``CONFIG_RCU_NOCB_CPU=y`` and booted with ``rcu_nocbs=1-63``, where
-CPUs 1 through 63 spin in tight loops that invoke ``call_rcu()``. Even
-if these tight loops also contain calls to ``cond_resched()`` (thus
+CPUs 1 through 63 spin in tight loops that invoke call_rcu(). Even
+if these tight loops also contain calls to cond_resched() (thus
allowing grace periods to complete), CPU 0 simply will not be able to
invoke callbacks as fast as the other 63 CPUs can register them, at
least not until the system runs out of memory. In both of these
periods:
#. If a grace period fails to complete within 100 milliseconds, RCU
- causes future invocations of ``cond_resched()`` on the holdout CPUs
+ causes future invocations of cond_resched() on the holdout CPUs
to provide an RCU quiescent state. RCU also causes those CPUs'
- ``need_resched()`` invocations to return ``true``, but only after the
+ need_resched() invocations to return ``true``, but only after the
corresponding CPU's next scheduling-clock.
#. CPUs mentioned in the ``nohz_full`` kernel boot parameter can run
indefinitely in the kernel without scheduling-clock interrupts, which
- defeats the above ``need_resched()`` strategem. RCU will therefore
- invoke ``resched_cpu()`` on any ``nohz_full`` CPUs still holding out
+ defeats the above need_resched() strategem. RCU will therefore
+ invoke resched_cpu() on any ``nohz_full`` CPUs still holding out
after 109 milliseconds.
#. In kernels built with ``CONFIG_RCU_BOOST=y``, if a given task that
has been preempted within an RCU read-side critical section is
holding out for more than 500 milliseconds, RCU will resort to
priority boosting.
#. If a CPU is still holding out 10 seconds into the grace period, RCU
- will invoke ``resched_cpu()`` on it regardless of its ``nohz_full``
+ will invoke resched_cpu() on it regardless of its ``nohz_full``
state.
The above values are defaults for systems running with ``HZ=1000``. They
are provided only for RCU, not for `SRCU <#Sleepable%20RCU>`__ or `Tasks
RCU <#Tasks%20RCU>`__.
-RCU takes the following steps in ``call_rcu()`` to encourage timely
+RCU takes the following steps in call_rcu() to encourage timely
invocation of callbacks when any given non-\ ``rcu_nocbs`` CPU has
10,000 callbacks, or has 10,000 more callbacks than it had the last time
encouragement was provided:
RCU <#Tasks%20RCU>`__. Even for RCU, callback-invocation forward
progress for ``rcu_nocbs`` CPUs is much less well-developed, in part
because workloads benefiting from ``rcu_nocbs`` CPUs tend to invoke
-``call_rcu()`` relatively infrequently. If workloads emerge that need
-both ``rcu_nocbs`` CPUs and high ``call_rcu()`` invocation rates, then
+call_rcu() relatively infrequently. If workloads emerge that need
+both ``rcu_nocbs`` CPUs and high call_rcu() invocation rates, then
additional forward-progress work will be required.
Composability
real-world implementations of composable constructs, there are
limitations.
-Implementations of RCU for which ``rcu_read_lock()`` and
-``rcu_read_unlock()`` generate no code, such as Linux-kernel RCU when
-``CONFIG_PREEMPT=n``, can be nested arbitrarily deeply. After all, there
+Implementations of RCU for which rcu_read_lock() and
+rcu_read_unlock() generate no code, such as Linux-kernel RCU when
+``CONFIG_PREEMPTION=n``, can be nested arbitrarily deeply. After all, there
is no overhead. Except that if all these instances of
-``rcu_read_lock()`` and ``rcu_read_unlock()`` are visible to the
+rcu_read_lock() and rcu_read_unlock() are visible to the
compiler, compilation will eventually fail due to exhausting memory,
mass storage, or user patience, whichever comes first. If the nesting is
not visible to the compiler, as is the case with mutually recursive
the fact remains that RCU must handle such workloads gracefully. This
requirement is another factor driving batching of grace periods, but it
is also the driving force behind the checks for large numbers of queued
-RCU callbacks in the ``call_rcu()`` code path. Finally, high update
+RCU callbacks in the call_rcu() code path. Finally, high update
rates should not delay RCU read-side critical sections, although some
small read-side delays can occur when using
-``synchronize_rcu_expedited()``, courtesy of this function's use of
-``smp_call_function_single()``.
+synchronize_rcu_expedited(), courtesy of this function's use of
+smp_call_function_single().
Although all three of these corner cases were understood in the early
1990s, a simple user-level test consisting of ``close(open(path))`` in a
Between Murphy's Law and “To err is human”, it is necessary to guard
against mishaps and misuse:
-#. It is all too easy to forget to use ``rcu_read_lock()`` everywhere
+#. It is all too easy to forget to use rcu_read_lock() everywhere
that it is needed, so kernels built with ``CONFIG_PROVE_RCU=y`` will
- splat if ``rcu_dereference()`` is used outside of an RCU read-side
+ splat if rcu_dereference() is used outside of an RCU read-side
critical section. Update-side code can use
- ``rcu_dereference_protected()``, which takes a `lockdep
+ rcu_dereference_protected(), which takes a `lockdep
expression <https://lwn.net/Articles/371986/>`__ to indicate what is
providing the protection. If the indicated protection is not
provided, a lockdep splat is emitted.
Code shared between readers and updaters can use
- ``rcu_dereference_check()``, which also takes a lockdep expression,
- and emits a lockdep splat if neither ``rcu_read_lock()`` nor the
+ rcu_dereference_check(), which also takes a lockdep expression,
+ and emits a lockdep splat if neither rcu_read_lock() nor the
indicated protection is in place. In addition,
- ``rcu_dereference_raw()`` is used in those (hopefully rare) cases
+ rcu_dereference_raw() is used in those (hopefully rare) cases
where the required protection cannot be easily described. Finally,
- ``rcu_read_lock_held()`` is provided to allow a function to verify
+ rcu_read_lock_held() is provided to allow a function to verify
that it has been invoked within an RCU read-side critical section. I
was made aware of this set of requirements shortly after Thomas
Gleixner audited a number of RCU uses.
#. A given function might wish to check for RCU-related preconditions
upon entry, before using any other RCU API. The
- ``rcu_lockdep_assert()`` does this job, asserting the expression in
+ rcu_lockdep_assert() does this job, asserting the expression in
kernels having lockdep enabled and doing nothing otherwise.
-#. It is also easy to forget to use ``rcu_assign_pointer()`` and
- ``rcu_dereference()``, perhaps (incorrectly) substituting a simple
+#. It is also easy to forget to use rcu_assign_pointer() and
+ rcu_dereference(), perhaps (incorrectly) substituting a simple
assignment. To catch this sort of error, a given RCU-protected
pointer may be tagged with ``__rcu``, after which sparse will
complain about simple-assignment accesses to that pointer. Arnd
Bergmann made me aware of this requirement, and also supplied the
needed `patch series <https://lwn.net/Articles/376011/>`__.
#. Kernels built with ``CONFIG_DEBUG_OBJECTS_RCU_HEAD=y`` will splat if
- a data element is passed to ``call_rcu()`` twice in a row, without a
+ a data element is passed to call_rcu() twice in a row, without a
grace period in between. (This error is similar to a double free.)
The corresponding ``rcu_head`` structures that are dynamically
allocated are automatically tracked, but ``rcu_head`` structures
allocated on the stack must be initialized with
- ``init_rcu_head_on_stack()`` and cleaned up with
- ``destroy_rcu_head_on_stack()``. Similarly, statically allocated
+ init_rcu_head_on_stack() and cleaned up with
+ destroy_rcu_head_on_stack(). Similarly, statically allocated
non-stack ``rcu_head`` structures must be initialized with
- ``init_rcu_head()`` and cleaned up with ``destroy_rcu_head()``.
+ init_rcu_head() and cleaned up with destroy_rcu_head().
Mathieu Desnoyers made me aware of this requirement, and also
supplied the needed
- `patch <https://lkml.kernel.org/g/20100319013024.GA28456@Krystal>`__.
+ `patch <https://lore.kernel.org/r/20100319013024.GA28456@Krystal>`__.
#. An infinite loop in an RCU read-side critical section will eventually
trigger an RCU CPU stall warning splat, with the duration of
“eventually” being controlled by the ``RCU_CPU_STALL_TIMEOUT``
``rcupdate.rcu_cpu_stall_suppress`` to suppress the splats. This
kernel parameter may also be set via ``sysfs``. Furthermore, RCU CPU
stall warnings are counter-productive during sysrq dumps and during
- panics. RCU therefore supplies the ``rcu_sysrq_start()`` and
- ``rcu_sysrq_end()`` API members to be called before and after long
- sysrq dumps. RCU also supplies the ``rcu_panic()`` notifier that is
+ panics. RCU therefore supplies the rcu_sysrq_start() and
+ rcu_sysrq_end() API members to be called before and after long
+ sysrq dumps. RCU also supplies the rcu_panic() notifier that is
automatically invoked at the beginning of a panic to suppress further
RCU CPU stall warnings.
synchronization mechanism, for example, reference counting.
#. In kernels built with ``CONFIG_RCU_TRACE=y``, RCU-related information
is provided via event tracing.
-#. Open-coded use of ``rcu_assign_pointer()`` and ``rcu_dereference()``
+#. Open-coded use of rcu_assign_pointer() and rcu_dereference()
to create typical linked data structures can be surprisingly
error-prone. Therefore, RCU-protected `linked
lists <https://lwn.net/Articles/609973/#RCU%20List%20APIs>`__ and,
other special-purpose RCU-protected data structures are available in
the Linux kernel and the userspace RCU library.
#. Some linked structures are created at compile time, but still require
- ``__rcu`` checking. The ``RCU_POINTER_INITIALIZER()`` macro serves
+ ``__rcu`` checking. The RCU_POINTER_INITIALIZER() macro serves
this purpose.
-#. It is not necessary to use ``rcu_assign_pointer()`` when creating
+#. It is not necessary to use rcu_assign_pointer() when creating
linked structures that are to be published via a single external
- pointer. The ``RCU_INIT_POINTER()`` macro is provided for this task
- and also for assigning ``NULL`` pointers at runtime.
+ pointer. The RCU_INIT_POINTER() macro is provided for this task.
This not a hard-and-fast list: RCU's diagnostic capabilities will
continue to be guided by the number and type of usage bugs found in
This all should be quite obvious, but the fact remains that Linus
Torvalds recently had to
-`remind <https://lkml.kernel.org/g/CA+55aFy4wcCwaL4okTs8wXhGZ5h-ibecy_Meg9C4MNQrUnwMcg@mail.gmail.com>`__
+`remind <https://lore.kernel.org/r/CA+55aFy4wcCwaL4okTs8wXhGZ5h-ibecy_Meg9C4MNQrUnwMcg@mail.gmail.com>`__
me of this requirement.
Firmware Interface
~~~~~~~~~~
The Linux kernel's boot sequence is an interesting process, and RCU is
-used early, even before ``rcu_init()`` is invoked. In fact, a number of
+used early, even before rcu_init() is invoked. In fact, a number of
RCU's primitives can be used as soon as the initial task's
``task_struct`` is available and the boot CPU's per-CPU variables are
-set up. The read-side primitives (``rcu_read_lock()``,
-``rcu_read_unlock()``, ``rcu_dereference()``, and
-``rcu_access_pointer()``) will operate normally very early on, as will
-``rcu_assign_pointer()``.
+set up. The read-side primitives (rcu_read_lock(),
+rcu_read_unlock(), rcu_dereference(), and
+rcu_access_pointer()) will operate normally very early on, as will
+rcu_assign_pointer().
-Although ``call_rcu()`` may be invoked at any time during boot,
+Although call_rcu() may be invoked at any time during boot,
callbacks are not guaranteed to be invoked until after all of RCU's
-kthreads have been spawned, which occurs at ``early_initcall()`` time.
+kthreads have been spawned, which occurs at early_initcall() time.
This delay in callback invocation is due to the fact that RCU does not
invoke callbacks until it is fully initialized, and this full
initialization cannot occur until after the scheduler has initialized
panacea because there would be severe restrictions on what operations
those callbacks could invoke.
-Perhaps surprisingly, ``synchronize_rcu()`` and
-``synchronize_rcu_expedited()``, will operate normally during very early
+Perhaps surprisingly, synchronize_rcu() and
+synchronize_rcu_expedited(), will operate normally during very early
boot, the reason being that there is only one CPU and preemption is
-disabled. This means that the call ``synchronize_rcu()`` (or friends)
+disabled. This means that the call synchronize_rcu() (or friends)
itself is a quiescent state and thus a grace period, so the early-boot
implementation can be a no-op.
However, once the scheduler has spawned its first kthread, this early
-boot trick fails for ``synchronize_rcu()`` (as well as for
-``synchronize_rcu_expedited()``) in ``CONFIG_PREEMPT=y`` kernels. The
+boot trick fails for synchronize_rcu() (as well as for
+synchronize_rcu_expedited()) in ``CONFIG_PREEMPTION=y`` kernels. The
reason is that an RCU read-side critical section might be preempted,
-which means that a subsequent ``synchronize_rcu()`` really does have to
+which means that a subsequent synchronize_rcu() really does have to
wait for something, as opposed to simply returning immediately.
-Unfortunately, ``synchronize_rcu()`` can't do this until all of its
+Unfortunately, synchronize_rcu() can't do this until all of its
kthreads are spawned, which doesn't happen until some time during
-``early_initcalls()`` time. But this is no excuse: RCU is nevertheless
+early_initcalls() time. But this is no excuse: RCU is nevertheless
required to correctly handle synchronous grace periods during this time
period. Once all of its kthreads are up and running, RCU starts running
normally.
The Linux kernel has interrupts, and RCU read-side critical sections are
legal within interrupt handlers and within interrupt-disabled regions of
-code, as are invocations of ``call_rcu()``.
+code, as are invocations of call_rcu().
Some Linux-kernel architectures can enter an interrupt handler from
non-idle process context, and then just never leave it, instead
The Linux kernel has non-maskable interrupts (NMIs), and RCU read-side
critical sections are legal within NMI handlers. Thankfully, RCU
-update-side primitives, including ``call_rcu()``, are prohibited within
+update-side primitives, including call_rcu(), are prohibited within
NMI handlers.
The name notwithstanding, some Linux-kernel architectures can have
nested NMIs, which RCU must handle correctly. Andy Lutomirski `surprised
-me <https://lkml.kernel.org/r/CALCETrXLq1y7e_dKFPgou-FKHB6Pu-r8+t-6Ds+8=va7anBWDA@mail.gmail.com>`__
+me <https://lore.kernel.org/r/CALCETrXLq1y7e_dKFPgou-FKHB6Pu-r8+t-6Ds+8=va7anBWDA@mail.gmail.com>`__
with this requirement; he also kindly surprised me with `an
-algorithm <https://lkml.kernel.org/r/CALCETrXSY9JpW3uE6H8WYk81sg56qasA2aqmjMPsq5dOtzso=g@mail.gmail.com>`__
+algorithm <https://lore.kernel.org/r/CALCETrXSY9JpW3uE6H8WYk81sg56qasA2aqmjMPsq5dOtzso=g@mail.gmail.com>`__
that meets this requirement.
Furthermore, NMI handlers can be interrupted by what appear to RCU to be
normal interrupts. One way that this can happen is for code that
-directly invokes ``rcu_irq_enter()`` and ``rcu_irq_exit()`` to be called
+directly invokes rcu_irq_enter() and rcu_irq_exit() to be called
from an NMI handler. This astonishing fact of life prompted the current
-code structure, which has ``rcu_irq_enter()`` invoking
-``rcu_nmi_enter()`` and ``rcu_irq_exit()`` invoking ``rcu_nmi_exit()``.
+code structure, which has rcu_irq_enter() invoking
+rcu_nmi_enter() and rcu_irq_exit() invoking rcu_nmi_exit().
And yes, I also learned of this requirement the hard way.
Loadable Modules
unloaded. After a given module has been unloaded, any attempt to call
one of its functions results in a segmentation fault. The module-unload
functions must therefore cancel any delayed calls to loadable-module
-functions, for example, any outstanding ``mod_timer()`` must be dealt
-with via ``del_timer_sync()`` or similar.
+functions, for example, any outstanding mod_timer() must be dealt
+with via del_timer_sync() or similar.
Unfortunately, there is no way to cancel an RCU callback; once you
-invoke ``call_rcu()``, the callback function is eventually going to be
+invoke call_rcu(), the callback function is eventually going to be
invoked, unless the system goes down first. Because it is normally
considered socially irresponsible to crash the system in response to a
module unload request, we need some other way to deal with in-flight RCU
callbacks.
-RCU therefore provides ``rcu_barrier()``, which waits until all
+RCU therefore provides rcu_barrier(), which waits until all
in-flight RCU callbacks have been invoked. If a module uses
-``call_rcu()``, its exit function should therefore prevent any future
-invocation of ``call_rcu()``, then invoke ``rcu_barrier()``. In theory,
-the underlying module-unload code could invoke ``rcu_barrier()``
+call_rcu(), its exit function should therefore prevent any future
+invocation of call_rcu(), then invoke rcu_barrier(). In theory,
+the underlying module-unload code could invoke rcu_barrier()
unconditionally, but in practice this would incur unacceptable
latencies.
Nikita Danilov noted this requirement for an analogous
filesystem-unmount situation, and Dipankar Sarma incorporated
-``rcu_barrier()`` into RCU. The need for ``rcu_barrier()`` for module
+rcu_barrier() into RCU. The need for rcu_barrier() for module
unloading became apparent later.
.. important::
- The ``rcu_barrier()`` function is not, repeat,
+ The rcu_barrier() function is not, repeat,
*not*, obligated to wait for a grace period. It is instead only required
to wait for RCU callbacks that have already been posted. Therefore, if
there are no RCU callbacks posted anywhere in the system,
- ``rcu_barrier()`` is within its rights to return immediately. Even if
- there are callbacks posted, ``rcu_barrier()`` does not necessarily need
+ rcu_barrier() is within its rights to return immediately. Even if
+ there are callbacks posted, rcu_barrier() does not necessarily need
to wait for a grace period.
+-----------------------------------------------------------------------+
| **Quick Quiz**: |
+-----------------------------------------------------------------------+
| Wait a minute! Each RCU callbacks must wait for a grace period to |
-| complete, and ``rcu_barrier()`` must wait for each pre-existing |
-| callback to be invoked. Doesn't ``rcu_barrier()`` therefore need to |
+| complete, and rcu_barrier() must wait for each pre-existing |
+| callback to be invoked. Doesn't rcu_barrier() therefore need to |
| wait for a full grace period if there is even one callback posted |
| anywhere in the system? |
+-----------------------------------------------------------------------+
| Absolutely not!!! |
| Yes, each RCU callbacks must wait for a grace period to complete, but |
| it might well be partly (or even completely) finished waiting by the |
-| time ``rcu_barrier()`` is invoked. In that case, ``rcu_barrier()`` |
+| time rcu_barrier() is invoked. In that case, rcu_barrier() |
| need only wait for the remaining portion of the grace period to |
| elapse. So even if there are quite a few callbacks posted, |
-| ``rcu_barrier()`` might well return quite quickly. |
+| rcu_barrier() might well return quite quickly. |
| |
| So if you need to wait for a grace period as well as for all |
| pre-existing callbacks, you will need to invoke both |
-| ``synchronize_rcu()`` and ``rcu_barrier()``. If latency is a concern, |
+| synchronize_rcu() and rcu_barrier(). If latency is a concern, |
| you can always use workqueues to invoke them concurrently. |
+-----------------------------------------------------------------------+
to allow the various kernel subsystems (including RCU) to respond
appropriately to a given CPU-hotplug operation. Most RCU operations may
be invoked from CPU-hotplug notifiers, including even synchronous
-grace-period operations such as (``synchronize_rcu()`` and
-``synchronize_rcu_expedited()``). However, these synchronous operations
+grace-period operations such as (synchronize_rcu() and
+synchronize_rcu_expedited()). However, these synchronous operations
do block and therefore cannot be invoked from notifiers that execute via
-``stop_machine()``, specifically those between the ``CPUHP_AP_OFFLINE``
+stop_machine(), specifically those between the ``CPUHP_AP_OFFLINE``
and ``CPUHP_AP_ONLINE`` states.
-In addition, all-callback-wait operations such as ``rcu_barrier()`` may
+In addition, all-callback-wait operations such as rcu_barrier() may
not be invoked from any CPU-hotplug notifier. This restriction is due
to the fact that there are phases of CPU-hotplug operations where the
outgoing CPU's callbacks will not be invoked until after the CPU-hotplug
operation ends, which could also result in deadlock. Furthermore,
-``rcu_barrier()`` blocks CPU-hotplug operations during its execution,
+rcu_barrier() blocks CPU-hotplug operations during its execution,
which results in another type of deadlock when invoked from a CPU-hotplug
notifier.
An offline CPU's quiescent state will be reported either:
-1. As the CPU goes offline using RCU's hotplug notifier (``rcu_report_dead()``).
-2. When grace period initialization (``rcu_gp_init()``) detects a
+1. As the CPU goes offline using RCU's hotplug notifier (rcu_report_dead()).
+2. When grace period initialization (rcu_gp_init()) detects a
race either with CPU offlining or with a task unblocking on a leaf
``rcu_node`` structure whose CPUs are all offline.
-The CPU-online path (``rcu_cpu_starting()``) should never need to report
+The CPU-online path (rcu_cpu_starting()) should never need to report
a quiescent state for an offline CPU. However, as a debugging measure,
it does emit a warning if a quiescent state was not already reported
for that CPU.
There is no longer any prohibition against holding any of
scheduler's runqueue or priority-inheritance spinlocks across an
-``rcu_read_unlock()``, even if interrupts and preemption were enabled
+rcu_read_unlock(), even if interrupts and preemption were enabled
somewhere within the corresponding RCU read-side critical section.
-Therefore, it is now perfectly legal to execute ``rcu_read_lock()``
+Therefore, it is now perfectly legal to execute rcu_read_lock()
with preemption enabled, acquire one of the scheduler locks, and hold
-that lock across the matching ``rcu_read_unlock()``.
+that lock across the matching rcu_read_unlock().
Similarly, the RCU flavor consolidation has removed the need for negative
nesting. The fact that interrupt-disabled regions of code act as RCU
~~~~~~~~~~~~~~~
It is possible to use tracing on RCU code, but tracing itself uses RCU.
-For this reason, ``rcu_dereference_raw_check()`` is provided for use
+For this reason, rcu_dereference_raw_check() is provided for use
by tracing, which avoids the destructive recursion that could otherwise
ensue. This API is also used by virtualization in some architectures,
where RCU readers execute in environments in which tracing cannot be
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The kernel needs to access user-space memory, for example, to access data
-referenced by system-call parameters. The ``get_user()`` macro does this job.
+referenced by system-call parameters. The get_user() macro does this job.
However, user-space memory might well be paged out, which means that
-``get_user()`` might well page-fault and thus block while waiting for the
+get_user() might well page-fault and thus block while waiting for the
resulting I/O to complete. It would be a very bad thing for the compiler to
-reorder a ``get_user()`` invocation into an RCU read-side critical section.
+reorder a get_user() invocation into an RCU read-side critical section.
For example, suppose that the source code looked like this:
5 rcu_read_unlock();
6 do_something_with(v, user_v);
-If the compiler did make this transformation in a ``CONFIG_PREEMPT=n`` kernel
-build, and if ``get_user()`` did page fault, the result would be a quiescent
+If the compiler did make this transformation in a ``CONFIG_PREEMPTION=n`` kernel
+build, and if get_user() did page fault, the result would be a quiescent
state in the middle of an RCU read-side critical section. This misplaced
quiescent state could result in line 4 being a use-after-free access,
which could be bad for your kernel's actuarial statistics. Similar examples
-can be constructed with the call to ``get_user()`` preceding the
-``rcu_read_lock()``.
+can be constructed with the call to get_user() preceding the
+rcu_read_lock().
-Unfortunately, ``get_user()`` doesn't have any particular ordering properties,
+Unfortunately, get_user() doesn't have any particular ordering properties,
and in some architectures the underlying ``asm`` isn't even marked
``volatile``. And even if it was marked ``volatile``, the above access to
``p->value`` is not volatile, so the compiler would not have any reason to keep
those two accesses in order.
-Therefore, the Linux-kernel definitions of ``rcu_read_lock()`` and
-``rcu_read_unlock()`` must act as compiler barriers, at least for outermost
-instances of ``rcu_read_lock()`` and ``rcu_read_unlock()`` within a nested set
+Therefore, the Linux-kernel definitions of rcu_read_lock() and
+rcu_read_unlock() must act as compiler barriers, at least for outermost
+instances of rcu_read_lock() and rcu_read_unlock() within a nested set
of RCU read-side critical sections.
Energy Efficiency
Because RCU avoids interrupting idle CPUs, it is illegal to execute an
RCU read-side critical section on an idle CPU. (Kernels built with
-``CONFIG_PROVE_RCU=y`` will splat if you try it.) The ``RCU_NONIDLE()``
+``CONFIG_PROVE_RCU=y`` will splat if you try it.) The RCU_NONIDLE()
macro and ``_rcuidle`` event tracing is provided to work around this
-restriction. In addition, ``rcu_is_watching()`` may be used to test
+restriction. In addition, rcu_is_watching() may be used to test
whether or not it is currently legal to run RCU read-side critical
sections on this CPU. I learned of the need for diagnostics on the one
-hand and ``RCU_NONIDLE()`` on the other while inspecting idle-loop code.
+hand and RCU_NONIDLE() on the other while inspecting idle-loop code.
Steven Rostedt supplied ``_rcuidle`` event tracing, which is used quite
heavily in the idle loop. However, there are some restrictions on the
-code placed within ``RCU_NONIDLE()``:
+code placed within RCU_NONIDLE():
#. Blocking is prohibited. In practice, this is not a serious
restriction given that idle tasks are prohibited from blocking to
begin with.
-#. Although nesting ``RCU_NONIDLE()`` is permitted, they cannot nest
+#. Although nesting RCU_NONIDLE() is permitted, they cannot nest
indefinitely deeply. However, given that they can be nested on the
order of a million deep, even on 32-bit systems, this should not be a
serious restriction. This nesting limit would probably be reached
long after the compiler OOMed or the stack overflowed.
-#. Any code path that enters ``RCU_NONIDLE()`` must sequence out of that
- same ``RCU_NONIDLE()``. For example, the following is grossly
+#. Any code path that enters RCU_NONIDLE() must sequence out of that
+ same RCU_NONIDLE(). For example, the following is grossly
illegal:
::
It is just as illegal to transfer control into the middle of
- ``RCU_NONIDLE()``'s argument. Yes, in theory, you could transfer in
+ RCU_NONIDLE()'s argument. Yes, in theory, you could transfer in
as long as you also transferred out, but in practice you could also
expect to get sharply worded review comments.
sections, and RCU believes this CPU to be idle, no problem. This
sort of thing is used by some architectures for light-weight
exception handlers, which can then avoid the overhead of
- ``rcu_irq_enter()`` and ``rcu_irq_exit()`` at exception entry and
+ rcu_irq_enter() and rcu_irq_exit() at exception entry and
exit, respectively. Some go further and avoid the entireties of
- ``irq_enter()`` and ``irq_exit()``.
+ irq_enter() and irq_exit().
Just make very sure you are running some of your tests with
``CONFIG_PROVE_RCU=y``, just in case one of your code paths was in
fact joking about not doing RCU read-side critical sections.
| **Quick Quiz**: |
+-----------------------------------------------------------------------+
| But what if my driver has a hardware interrupt handler that can run |
-| for many seconds? I cannot invoke ``schedule()`` from an hardware |
+| for many seconds? I cannot invoke schedule() from an hardware |
| interrupt handler, after all! |
+-----------------------------------------------------------------------+
| **Answer**: |
Although small-memory non-realtime systems can simply use Tiny RCU, code
size is only one aspect of memory efficiency. Another aspect is the size
-of the ``rcu_head`` structure used by ``call_rcu()`` and
-``kfree_rcu()``. Although this structure contains nothing more than a
+of the ``rcu_head`` structure used by call_rcu() and
+kfree_rcu(). Although this structure contains nothing more than a
pair of pointers, it does appear in many RCU-protected data structures,
including some that are size critical. The ``page`` structure is a case
in point, as evidenced by the many occurrences of the ``union`` keyword
singly linked lists to track the ``rcu_head`` structures that are
waiting for a grace period to elapse. It is also the reason why
``rcu_head`` structures do not contain debug information, such as fields
-tracking the file and line of the ``call_rcu()`` or ``kfree_rcu()`` that
+tracking the file and line of the call_rcu() or kfree_rcu() that
posted them. Although this information might appear in debug-only kernel
builds at some point, in the meantime, the ``->func`` field will often
provide the needed debug information.
``rcu_head`` field shares storage with a great many other structures
that are used at various points in the corresponding page's lifetime. In
order to correctly resolve certain `race
-conditions <https://lkml.kernel.org/g/1439976106-137226-1-git-send-email-kirill.shutemov@linux.intel.com>`__,
+conditions <https://lore.kernel.org/r/1439976106-137226-1-git-send-email-kirill.shutemov@linux.intel.com>`__,
the Linux kernel's memory-management subsystem needs a particular bit to
remain zero during all phases of grace-period processing, and that bit
happens to map to the bottom bit of the ``rcu_head`` structure's
-``->next`` field. RCU makes this guarantee as long as ``call_rcu()`` is
-used to post the callback, as opposed to ``kfree_rcu()`` or some future
-“lazy” variant of ``call_rcu()`` that might one day be created for
+``->next`` field. RCU makes this guarantee as long as call_rcu() is
+used to post the callback, as opposed to kfree_rcu() or some future
+“lazy” variant of call_rcu() that might one day be created for
energy-efficiency purposes.
That said, there are limits. RCU requires that the ``rcu_head``
structure be aligned to a two-byte boundary, and passing a misaligned
-``rcu_head`` structure to one of the ``call_rcu()`` family of functions
+``rcu_head`` structure to one of the call_rcu() family of functions
will result in a splat. It is therefore necessary to exercise caution
when packing structures containing fields of type ``rcu_head``. Why not
a four-byte or even eight-byte alignment requirement? Because the m68k
networking, security, virtualization, and scheduling code paths. RCU
must therefore use efficient implementations, especially in its
read-side primitives. To that end, it would be good if preemptible RCU's
-implementation of ``rcu_read_lock()`` could be inlined, however, doing
+implementation of rcu_read_lock() could be inlined, however, doing
this requires resolving ``#include`` issues with the ``task_struct``
structure.
continuously invoking any combination of RCU's runtime primitives with
minimal per-operation overhead. In fact, in many cases, increasing load
must *decrease* the per-operation overhead, witness the batching
-optimizations for ``synchronize_rcu()``, ``call_rcu()``,
-``synchronize_rcu_expedited()``, and ``rcu_barrier()``. As a general
+optimizations for synchronize_rcu(), call_rcu(),
+synchronize_rcu_expedited(), and rcu_barrier(). As a general
rule, RCU must cheerfully accept whatever the rest of the Linux kernel
decides to throw at it.
The Linux kernel is used for real-time workloads, especially in
conjunction with the `-rt
-patchset <https://rt.wiki.kernel.org/index.php/Main_Page>`__. The
+patchset <https://wiki.linuxfoundation.org/realtime/>`__. The
real-time-latency response requirements are such that the traditional
approach of disabling preemption across RCU read-side critical sections
-is inappropriate. Kernels built with ``CONFIG_PREEMPT=y`` therefore use
+is inappropriate. Kernels built with ``CONFIG_PREEMPTION=y`` therefore use
an RCU implementation that allows RCU read-side critical sections to be
preempted. This requirement made its presence known after users made it
clear that an earlier `real-time
patch <https://lwn.net/Articles/107930/>`__ did not meet their needs, in
conjunction with some `RCU
-issues <https://lkml.kernel.org/g/20050318002026.GA2693@us.ibm.com>`__
+issues <https://lore.kernel.org/r/20050318002026.GA2693@us.ibm.com>`__
encountered by a very early version of the -rt patchset.
In addition, RCU must make do with a sub-100-microsecond real-time
RCU must avoid degrading real-time response for CPU-bound threads,
whether executing in usermode (which is one use case for
``CONFIG_NO_HZ_FULL=y``) or in the kernel. That said, CPU-bound loops in
-the kernel must execute ``cond_resched()`` at least once per few tens of
+the kernel must execute cond_resched() at least once per few tens of
milliseconds in order to avoid receiving an IPI from RCU.
Finally, RCU's status as a synchronization primitive means that any RCU
condition and a system hang.
The solution was the creation of RCU-bh, which does
-``local_bh_disable()`` across its read-side critical sections, and which
+local_bh_disable() across its read-side critical sections, and which
uses the transition from one type of softirq processing to another as a
quiescent state in addition to context switch, idle, user mode, and
offline. This means that RCU-bh grace periods can complete even when
algorithms based on RCU-bh to withstand network-based denial-of-service
attacks.
-Because ``rcu_read_lock_bh()`` and ``rcu_read_unlock_bh()`` disable and
+Because rcu_read_lock_bh() and rcu_read_unlock_bh() disable and
re-enable softirq handlers, any attempt to start a softirq handlers
during the RCU-bh read-side critical section will be deferred. In this
-case, ``rcu_read_unlock_bh()`` will invoke softirq processing, which can
+case, rcu_read_unlock_bh() will invoke softirq processing, which can
take considerable time. One can of course argue that this softirq
overhead should be associated with the code following the RCU-bh
-read-side critical section rather than ``rcu_read_unlock_bh()``, but the
+read-side critical section rather than rcu_read_unlock_bh(), but the
fact is that most profiling tools cannot be expected to make this sort
of fine distinction. For example, suppose that a three-millisecond-long
RCU-bh read-side critical section executes during a time of heavy
networking load. There will very likely be an attempt to invoke at least
one softirq handler during that three milliseconds, but any such
invocation will be delayed until the time of the
-``rcu_read_unlock_bh()``. This can of course make it appear at first
-glance as if ``rcu_read_unlock_bh()`` was executing very slowly.
+rcu_read_unlock_bh(). This can of course make it appear at first
+glance as if rcu_read_unlock_bh() was executing very slowly.
The `RCU-bh
API <https://lwn.net/Articles/609973/#RCU%20Per-Flavor%20API%20Table>`__
-includes ``rcu_read_lock_bh()``, ``rcu_read_unlock_bh()``,
-``rcu_dereference_bh()``, ``rcu_dereference_bh_check()``,
-``synchronize_rcu_bh()``, ``synchronize_rcu_bh_expedited()``,
-``call_rcu_bh()``, ``rcu_barrier_bh()``, and
-``rcu_read_lock_bh_held()``. However, the update-side APIs are now
-simple wrappers for other RCU flavors, namely RCU-sched in
-CONFIG_PREEMPT=n kernels and RCU-preempt otherwise.
+includes rcu_read_lock_bh(), rcu_read_unlock_bh(), rcu_dereference_bh(),
+rcu_dereference_bh_check(), and rcu_read_lock_bh_held(). However, the
+old RCU-bh update-side APIs are now gone, replaced by synchronize_rcu(),
+synchronize_rcu_expedited(), call_rcu(), and rcu_barrier(). In addition,
+anything that disables bottom halves also marks an RCU-bh read-side
+critical section, including local_bh_disable() and local_bh_enable(),
+local_irq_save() and local_irq_restore(), and so on.
Sched Flavor (Historical)
~~~~~~~~~~~~~~~~~~~~~~~~~
RCU read-side critical section can be a quiescent state. Therefore,
*RCU-sched* was created, which follows “classic” RCU in that an
RCU-sched grace period waits for pre-existing interrupt and NMI
-handlers. In kernels built with ``CONFIG_PREEMPT=n``, the RCU and
+handlers. In kernels built with ``CONFIG_PREEMPTION=n``, the RCU and
RCU-sched APIs have identical implementations, while kernels built with
-``CONFIG_PREEMPT=y`` provide a separate implementation for each.
+``CONFIG_PREEMPTION=y`` provide a separate implementation for each.
-Note well that in ``CONFIG_PREEMPT=y`` kernels,
-``rcu_read_lock_sched()`` and ``rcu_read_unlock_sched()`` disable and
+Note well that in ``CONFIG_PREEMPTION=y`` kernels,
+rcu_read_lock_sched() and rcu_read_unlock_sched() disable and
re-enable preemption, respectively. This means that if there was a
preemption attempt during the RCU-sched read-side critical section,
-``rcu_read_unlock_sched()`` will enter the scheduler, with all the
-latency and overhead entailed. Just as with ``rcu_read_unlock_bh()``,
-this can make it look as if ``rcu_read_unlock_sched()`` was executing
+rcu_read_unlock_sched() will enter the scheduler, with all the
+latency and overhead entailed. Just as with rcu_read_unlock_bh(),
+this can make it look as if rcu_read_unlock_sched() was executing
very slowly. However, the highest-priority task won't be preempted, so
-that task will enjoy low-overhead ``rcu_read_unlock_sched()``
+that task will enjoy low-overhead rcu_read_unlock_sched()
invocations.
The `RCU-sched
API <https://lwn.net/Articles/609973/#RCU%20Per-Flavor%20API%20Table>`__
-includes ``rcu_read_lock_sched()``, ``rcu_read_unlock_sched()``,
-``rcu_read_lock_sched_notrace()``, ``rcu_read_unlock_sched_notrace()``,
-``rcu_dereference_sched()``, ``rcu_dereference_sched_check()``,
-``synchronize_sched()``, ``synchronize_rcu_sched_expedited()``,
-``call_rcu_sched()``, ``rcu_barrier_sched()``, and
-``rcu_read_lock_sched_held()``. However, anything that disables
-preemption also marks an RCU-sched read-side critical section, including
-``preempt_disable()`` and ``preempt_enable()``, ``local_irq_save()`` and
-``local_irq_restore()``, and so on.
+includes rcu_read_lock_sched(), rcu_read_unlock_sched(),
+rcu_read_lock_sched_notrace(), rcu_read_unlock_sched_notrace(),
+rcu_dereference_sched(), rcu_dereference_sched_check(), and
+rcu_read_lock_sched_held(). However, the old RCU-sched update-side APIs
+are now gone, replaced by synchronize_rcu(), synchronize_rcu_expedited(),
+call_rcu(), and rcu_barrier(). In addition, anything that disables
+preemption also marks an RCU-sched read-side critical section,
+including preempt_disable() and preempt_enable(), local_irq_save()
+and local_irq_restore(), and so on.
Sleepable RCU
~~~~~~~~~~~~~
structure. The key benefit of these domains is that a slow SRCU reader
in one domain does not delay an SRCU grace period in some other domain.
That said, one consequence of these domains is that read-side code must
-pass a “cookie” from ``srcu_read_lock()`` to ``srcu_read_unlock()``, for
+pass a “cookie” from srcu_read_lock() to srcu_read_unlock(), for
example, as follows:
::
6 srcu_read_unlock(&ss, idx);
However, if line 5 acquired a mutex that was held across a
-``synchronize_srcu()`` for domain ``ss``, deadlock would still be
+synchronize_srcu() for domain ``ss``, deadlock would still be
possible. Furthermore, if line 5 acquired a mutex that was held across a
-``synchronize_srcu()`` for some other domain ``ss1``, and if an
+synchronize_srcu() for some other domain ``ss1``, and if an
``ss1``-domain SRCU read-side critical section acquired another mutex
-that was held across as ``ss``-domain ``synchronize_srcu()``, deadlock
+that was held across as ``ss``-domain synchronize_srcu(), deadlock
would again be possible. Such a deadlock cycle could extend across an
arbitrarily large number of different SRCU domains. Again, with great
power comes great responsibility.
Unlike the other RCU flavors, SRCU read-side critical sections can run
on idle and even offline CPUs. This ability requires that
-``srcu_read_lock()`` and ``srcu_read_unlock()`` contain memory barriers,
+srcu_read_lock() and srcu_read_unlock() contain memory barriers,
which means that SRCU readers will run a bit slower than would RCU
-readers. It also motivates the ``smp_mb__after_srcu_read_unlock()`` API,
-which, in combination with ``srcu_read_unlock()``, guarantees a full
+readers. It also motivates the smp_mb__after_srcu_read_unlock() API,
+which, in combination with srcu_read_unlock(), guarantees a full
memory barrier.
-Also unlike other RCU flavors, ``synchronize_srcu()`` may **not** be
+Also unlike other RCU flavors, synchronize_srcu() may **not** be
invoked from CPU-hotplug notifiers, due to the fact that SRCU grace
periods make use of timers and the possibility of timers being
temporarily “stranded” on the outgoing CPU. This stranding of timers
an SRCU grace period, that grace period is waiting on a timer, and that
timer is stranded on the outgoing CPU, then the notifier will never be
awakened, in other words, deadlock has occurred. This same situation of
-course also prohibits ``srcu_barrier()`` from being invoked from
+course also prohibits srcu_barrier() from being invoked from
CPU-hotplug notifiers.
SRCU also differs from other RCU flavors in that SRCU's expedited and
current implementation, not necessarily of future implementations.) In
addition, if SRCU has been idle for longer than the interval specified
by the ``srcutree.exp_holdoff`` kernel boot parameter (25 microseconds
-by default), and if a ``synchronize_srcu()`` invocation ends this idle
+by default), and if a synchronize_srcu() invocation ends this idle
period, that invocation will be automatically expedited.
As of v4.12, SRCU's callbacks are maintained per-CPU, eliminating a
locking bottleneck present in prior kernel versions. Although this will
-allow users to put much heavier stress on ``call_srcu()``, it is
+allow users to put much heavier stress on call_srcu(), it is
important to note that SRCU does not yet take any special steps to deal
with callback flooding. So if you are posting (say) 10,000 SRCU
callbacks per second per CPU, you are probably totally OK, but if you
The `SRCU
API <https://lwn.net/Articles/609973/#RCU%20Per-Flavor%20API%20Table>`__
-includes ``srcu_read_lock()``, ``srcu_read_unlock()``,
-``srcu_dereference()``, ``srcu_dereference_check()``,
-``synchronize_srcu()``, ``synchronize_srcu_expedited()``,
-``call_srcu()``, ``srcu_barrier()``, and ``srcu_read_lock_held()``. It
-also includes ``DEFINE_SRCU()``, ``DEFINE_STATIC_SRCU()``, and
-``init_srcu_struct()`` APIs for defining and initializing
+includes srcu_read_lock(), srcu_read_unlock(),
+srcu_dereference(), srcu_dereference_check(),
+synchronize_srcu(), synchronize_srcu_expedited(),
+call_srcu(), srcu_barrier(), and srcu_read_lock_held(). It
+also includes DEFINE_SRCU(), DEFINE_STATIC_SRCU(), and
+init_srcu_struct() APIs for defining and initializing
``srcu_struct`` structures.
+More recently, the SRCU API has added polling interfaces:
+
+#. start_poll_synchronize_srcu() returns a cookie identifying
+ the completion of a future SRCU grace period and ensures
+ that this grace period will be started.
+#. poll_state_synchronize_srcu() returns ``true`` iff the
+ specified cookie corresponds to an already-completed
+ SRCU grace period.
+#. get_state_synchronize_srcu() returns a cookie just like
+ start_poll_synchronize_srcu() does, but differs in that
+ it does nothing to ensure that any future SRCU grace period
+ will be started.
+
+These functions are used to avoid unnecessary SRCU grace periods in
+certain types of buffer-cache algorithms having multi-stage age-out
+mechanisms. The idea is that by the time the block has aged completely
+from the cache, an SRCU grace period will be very likely to have elapsed.
+
Tasks RCU
~~~~~~~~~
able to free old trampolines, which sounds like a job for some form of
RCU. However, because it is necessary to be able to install a trace
anywhere in the code, it is not possible to use read-side markers such
-as ``rcu_read_lock()`` and ``rcu_read_unlock()``. In addition, it does
+as rcu_read_lock() and rcu_read_unlock(). In addition, it does
not work to have these markers in the trampoline itself, because there
-would need to be instructions following ``rcu_read_unlock()``. Although
-``synchronize_rcu()`` would guarantee that execution reached the
-``rcu_read_unlock()``, it would not be able to guarantee that execution
+would need to be instructions following rcu_read_unlock(). Although
+synchronize_rcu() would guarantee that execution reached the
+rcu_read_unlock(), it would not be able to guarantee that execution
had completely left the trampoline. Worse yet, in some situations
the trampoline's protection must extend a few instructions *prior* to
execution reaching the trampoline. For example, these few instructions
The solution, in the form of `Tasks
RCU <https://lwn.net/Articles/607117/>`__, is to have implicit read-side
critical sections that are delimited by voluntary context switches, that
-is, calls to ``schedule()``, ``cond_resched()``, and
-``synchronize_rcu_tasks()``. In addition, transitions to and from
+is, calls to schedule(), cond_resched(), and
+synchronize_rcu_tasks(). In addition, transitions to and from
userspace execution also delimit tasks-RCU read-side critical sections.
The tasks-RCU API is quite compact, consisting only of
-``call_rcu_tasks()``, ``synchronize_rcu_tasks()``, and
-``rcu_barrier_tasks()``. In ``CONFIG_PREEMPT=n`` kernels, trampolines
-cannot be preempted, so these APIs map to ``call_rcu()``,
-``synchronize_rcu()``, and ``rcu_barrier()``, respectively. In
-``CONFIG_PREEMPT=y`` kernels, trampolines can be preempted, and these
+call_rcu_tasks(), synchronize_rcu_tasks(), and
+rcu_barrier_tasks(). In ``CONFIG_PREEMPTION=n`` kernels, trampolines
+cannot be preempted, so these APIs map to call_rcu(),
+synchronize_rcu(), and rcu_barrier(), respectively. In
+``CONFIG_PREEMPTION=y`` kernels, trampolines can be preempted, and these
three APIs are therefore implemented by separate functions that check
for voluntary context switches.
latency.
RCU disables CPU hotplug in a few places, perhaps most notably in the
-``rcu_barrier()`` operations. If there is a strong reason to use
-``rcu_barrier()`` in CPU-hotplug notifiers, it will be necessary to
+rcu_barrier() operations. If there is a strong reason to use
+rcu_barrier() in CPU-hotplug notifiers, it will be necessary to
avoid disabling CPU hotplug. This would introduce some complexity, so
there had better be a *very* good reason.
nodes nor does it align the CPU groups with hardware features such as
sockets or cores. Such spreading and alignment is currently believed to
be unnecessary because the hotpath read-side primitives do not access
-the combining tree, nor does ``call_rcu()`` in the common case. If you
+the combining tree, nor does call_rcu() in the common case. If you
believe that your architecture needs such spreading and alignment, then
your architecture should also benefit from the
``rcutree.rcu_fanout_leaf`` boot parameter, which can be set to the
extreme loads. It might also be necessary to be able to relate CPU
utilization by RCU's kthreads and softirq handlers to the code that
instigated this CPU utilization. For example, RCU callback overhead
-might be charged back to the originating ``call_rcu()`` instance, though
+might be charged back to the originating call_rcu() instance, though
probably not in production kernels.
Additional work may be required to provide reasonable forward-progress
is less readable and prevents lockdep from detecting locking issues.
Letting RCU-protected pointers "leak" out of an RCU read-side
- critical section is every bid as bad as letting them leak out
+ critical section is every bit as bad as letting them leak out
from under a lock. Unless, of course, you have arranged some
other means of protection, such as a lock or a reference count
-before- letting them out of the RCU read-side critical section.
accesses. The rcu_dereference() primitive ensures that
the CPU picks up the pointer before it picks up the data
that the pointer points to. This really is necessary
- on Alpha CPUs. If you don't believe me, see:
-
- http://www.openvms.compaq.com/wizard/wiz_2637.html
+ on Alpha CPUs.
The rcu_dereference() primitive is also an excellent
documentation aid, letting the person reading the
the rest of the system.
7. As of v4.20, a given kernel implements only one RCU flavor,
- which is RCU-sched for PREEMPT=n and RCU-preempt for PREEMPT=y.
+ which is RCU-sched for PREEMPTION=n and RCU-preempt for PREEMPTION=y.
If the updater uses call_rcu() or synchronize_rcu(),
- then the corresponding readers my use rcu_read_lock() and
+ then the corresponding readers may use rcu_read_lock() and
rcu_read_unlock(), rcu_read_lock_bh() and rcu_read_unlock_bh(),
or any pair of primitives that disables and re-enables preemption,
for example, rcu_read_lock_sched() and rcu_read_unlock_sched().
of as a replacement for read-writer locking (among other things), but with
very low-overhead readers that are immune to deadlock, priority inversion,
and unbounded latency. RCU read-side critical sections are delimited
-by rcu_read_lock() and rcu_read_unlock(), which, in non-CONFIG_PREEMPT
+by rcu_read_lock() and rcu_read_unlock(), which, in non-CONFIG_PREEMPTION
kernels, generate no code whatsoever.
This means that RCU writers are unaware of the presence of concurrent
to smp_call_function() and further to smp_call_function_on_cpu(),
causing this latter to spin until the cross-CPU invocation of
rcu_barrier_func() has completed. This by itself would prevent
- a grace period from completing on non-CONFIG_PREEMPT kernels,
+ a grace period from completing on non-CONFIG_PREEMPTION kernels,
since each CPU must undergo a context switch (or other quiescent
state) before the grace period can complete. However, this is
- of no use in CONFIG_PREEMPT kernels.
+ of no use in CONFIG_PREEMPTION kernels.
Therefore, on_each_cpu() disables preemption across its call
to smp_call_function() and also across the local call to
- A CPU looping with bottom halves disabled.
-- For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel
+- For !CONFIG_PREEMPTION kernels, a CPU looping anywhere in the kernel
without invoking schedule(). If the looping in the kernel is
really expected and desirable behavior, you might need to add
some calls to cond_resched().
result in the ``rcu_.*kthread starved for`` console-log message,
which will include additional debugging information.
-- A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might
+- A CPU-bound real-time task in a CONFIG_PREEMPTION kernel, which might
happen to preempt a low-priority task in the middle of an RCU
read-side critical section. This is especially damaging if
that low-priority task is not permitted to run on any other CPU,
buggy timer hardware through bugs in the interrupt or exception
path (whether hardware, firmware, or software) through bugs
in Linux's timer subsystem through bugs in the scheduler, and,
- yes, even including bugs in RCU itself.
+ yes, even including bugs in RCU itself. It can also result in
+ the ``rcu_.*timer wakeup didn't happen for`` console-log message,
+ which will include additional debugging information.
- A bug in the RCU implementation.
task_struct ->state field, and the "cpu" indicates that the grace-period
kthread last ran on CPU 5.
+If the relevant grace-period kthread does not wake from FQS wait in a
+reasonable time, then the following additional line is printed::
+
+ kthread timer wakeup didn't happen for 23804 jiffies! g7076 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
+
+The "23804" indicates that kthread's timer expired more than 23 thousand
+jiffies ago. The rest of the line has meaning similar to the kthread
+starvation case.
+
+Additionally, the following line is printed::
+
+ Possible timer handling issue on cpu=4 timer-softirq=11142
+
+Here "cpu" indicates that the grace-period kthread last ran on CPU 4,
+where it queued the fqs timer. The number following the "timer-softirq"
+is the current ``TIMER_SOFTIRQ`` count on cpu 4. If this value does not
+change on successive RCU CPU stall warnings, there is further reason to
+suspect a timer problem.
+
Multiple Warnings From One Stall
================================
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This section presents a "toy" RCU implementation that is based on
"classic RCU". It is also short on performance (but only for updates) and
-on features such as hotplug CPU and the ability to run in CONFIG_PREEMPT
+on features such as hotplug CPU and the ability to run in CONFIG_PREEMPTION
kernels. The definitions of rcu_dereference() and rcu_assign_pointer()
are the same as those shown in the preceding section, so they are omitted.
::
Quick Quiz #3:
If it is illegal to block in an RCU read-side
critical section, what the heck do you do in
- PREEMPT_RT, where normal spinlocks can block???
+ CONFIG_PREEMPT_RT, where normal spinlocks can block???
:ref:`Answers to Quick Quiz <8_whatisRCU>`
overhead is **negative**.
Answer:
- Imagine a single-CPU system with a non-CONFIG_PREEMPT
+ Imagine a single-CPU system with a non-CONFIG_PREEMPTION
kernel where a routing table is used by process-context
code, but can be updated by irq-context code (for example,
by an "ICMP REDIRECT" packet). The usual way of handling
Quick Quiz #3:
If it is illegal to block in an RCU read-side
critical section, what the heck do you do in
- PREEMPT_RT, where normal spinlocks can block???
+ CONFIG_PREEMPT_RT, where normal spinlocks can block???
Answer:
- Just as PREEMPT_RT permits preemption of spinlock
+ Just as CONFIG_PREEMPT_RT permits preemption of spinlock
critical sections, it permits preemption of RCU
read-side critical sections. It also permits
spinlocks blocking while in RCU read-side critical
value, meaning that RCU_SOFTIRQ is used by default.
Specify rcutree.use_softirq=0 to use rcuc kthreads.
+ But note that CONFIG_PREEMPT_RT=y kernels disable
+ this kernel boot parameter, forcibly setting it
+ to zero.
+
rcutree.rcu_fanout_exact= [KNL]
Disable autobalancing of the rcu_node combining
tree. This is used by rcutorture, and might
Set wakeup interval for idle CPUs that have
RCU callbacks (RCU_FAST_NO_HZ=y).
- rcutree.rcu_idle_lazy_gp_delay= [KNL]
- Set wakeup interval for idle CPUs that have
- only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
- Lazy RCU callbacks are those which RCU can
- prove do nothing more than free memory.
-
rcutree.rcu_kick_kthreads= [KNL]
Cause the grace-period kthread to get an extra
wake_up() if it sleeps three times longer than
only normal grace-period primitives. No effect
on CONFIG_TINY_RCU kernels.
+ But note that CONFIG_PREEMPT_RT=y kernels enables
+ this kernel boot parameter, forcibly setting
+ it to the value one, that is, converting any
+ post-boot attempt at an expedited RCU grace
+ period to instead use normal non-expedited
+ grace-period processing.
+
rcupdate.rcu_task_ipi_delay= [KNL]
Set time in jiffies during which RCU tasks will
avoid sending IPIs, starting with the beginning
refscale.verbose= [KNL]
Enable additional printk() statements.
+ refscale.verbose_batched= [KNL]
+ Batch the additional printk() statements. If zero
+ (the default) or negative, print everything. Otherwise,
+ print every Nth verbose statement, where N is the value
+ specified.
+
relax_domain_level=
[KNL, SMP] Set scheduler's default relax_domain_level.
See Documentation/admin-guide/cgroup-v1/cpusets.rst.
are running concurrently, especially on systems
with rotating-rust storage.
+ torture.verbose_sleep_frequency= [KNL]
+ Specifies how many verbose printk()s should be
+ emitted between each sleep. The default of zero
+ disables verbose-printk() sleeping.
+
+ torture.verbose_sleep_duration= [KNL]
+ Duration of each verbose-printk() sleep in jiffies.
+
tp720= [HW,PS2]
tpm_suspend_pcr=[HW,TPM]
}
/**
- * hlist_add_behing - add a new entry after the one specified
+ * hlist_add_behind - add a new entry after the one specified
* @n: new entry to be added
* @prev: hlist node to add it after, which must be non-NULL
*/
extern int sysctl_nr_trim_pages;
+void mem_dump_obj(void *object);
+
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */
#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
#define ulong2long(a) (*(long *)(&(a)))
+#define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
+#define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b)))
/* Exported common interfaces */
void call_rcu(struct rcu_head *head, rcu_callback_t func);
void rcu_report_dead(unsigned int cpu);
void rcutree_migrate_callbacks(int cpu);
+#ifdef CONFIG_TASKS_RCU_GENERIC
+void rcu_init_tasks_generic(void);
+#else
+static inline void rcu_init_tasks_generic(void) { }
+#endif
+
#ifdef CONFIG_RCU_STALL_COMMON
void rcu_sysrq_start(void);
void rcu_sysrq_end(void);
*/
#define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
-/*
- * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
- */
-#define __kvfree_rcu(head, offset) \
- do { \
- BUILD_BUG_ON(!__is_kvfree_rcu_offset(offset)); \
- kvfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
- } while (0)
-
/**
* kfree_rcu() - kfree an object after a grace period.
- * @ptr: pointer to kfree
- * @rhf: the name of the struct rcu_head within the type of @ptr.
+ * @ptr: pointer to kfree for both single- and double-argument invocations.
+ * @rhf: the name of the struct rcu_head within the type of @ptr,
+ * but only for double-argument invocations.
*
* Many rcu callbacks functions just call kfree() on the base structure.
* These functions are trivial, but their size adds up, and furthermore
* Because the functions are not allowed in the low-order 4096 bytes of
* kernel virtual memory, offsets up to 4095 bytes can be accommodated.
* If the offset is larger than 4095 bytes, a compile-time error will
- * be generated in __kvfree_rcu(). If this error is triggered, you can
+ * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
* either fall back to use of call_rcu() or rearrange the structure to
* position the rcu_head structure into the first 4096 bytes.
*
* The BUILD_BUG_ON check must not involve any function calls, hence the
* checks are done in macros here.
*/
-#define kfree_rcu(ptr, rhf) \
-do { \
- typeof (ptr) ___p = (ptr); \
- \
- if (___p) \
- __kvfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
-} while (0)
+#define kfree_rcu kvfree_rcu
/**
* kvfree_rcu() - kvfree an object after a grace period.
kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
#define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
-#define kvfree_rcu_arg_2(ptr, rhf) kfree_rcu(ptr, rhf)
+#define kvfree_rcu_arg_2(ptr, rhf) \
+do { \
+ typeof (ptr) ___p = (ptr); \
+ \
+ if (___p) { \
+ BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \
+ kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long) \
+ (offsetof(typeof(*(ptr)), rhf))); \
+ } \
+} while (0)
+
#define kvfree_rcu_arg_1(ptr) \
do { \
typeof(ptr) ___p = (ptr); \
void kfree_sensitive(const void *);
size_t __ksize(const void *);
size_t ksize(const void *);
+bool kmem_valid_obj(void *object);
+void kmem_dump_obj(void *object);
#ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
void synchronize_srcu(struct srcu_struct *ssp);
+unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
+unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
+bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct srcu_struct {
short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
- short srcu_idx; /* Current reader array element. */
+ unsigned short srcu_idx; /* Current reader array element in bit 0x2. */
+ unsigned short srcu_idx_max; /* Furthest future srcu_idx request. */
u8 srcu_gp_running; /* GP workqueue running? */
u8 srcu_gp_waiting; /* GP waiting for readers? */
struct swait_queue_head srcu_wq;
{
int idx;
- idx = READ_ONCE(ssp->srcu_idx);
+ idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
return idx;
}
{
int idx;
- idx = READ_ONCE(ssp->srcu_idx) & 0x1;
+ idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
tt, tf, idx,
READ_ONCE(ssp->srcu_lock_nesting[!idx]),
#define TOROUT_STRING(s) \
pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s)
#define VERBOSE_TOROUT_STRING(s) \
- do { if (verbose) pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s); } while (0)
+do { \
+ if (verbose) { \
+ verbose_torout_sleep(); \
+ pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s); \
+ } \
+} while (0)
#define VERBOSE_TOROUT_ERRSTRING(s) \
- do { if (verbose) pr_alert("%s" TORTURE_FLAG "!!! %s\n", torture_type, s); } while (0)
+do { \
+ if (verbose) { \
+ verbose_torout_sleep(); \
+ pr_alert("%s" TORTURE_FLAG "!!! %s\n", torture_type, s); \
+ } \
+} while (0)
+void verbose_torout_sleep(void);
/* Definitions for online/offline exerciser. */
+#ifdef CONFIG_HOTPLUG_CPU
+int torture_num_online_cpus(void);
+#else /* #ifdef CONFIG_HOTPLUG_CPU */
+static inline int torture_num_online_cpus(void) { return 1; }
+#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
typedef void torture_ofl_func(void);
bool torture_offline(int cpu, long *n_onl_attempts, long *n_onl_successes,
unsigned long *sum_offl, int *min_onl, int *max_onl);
trsp->trs_count = 0;
}
+/* Definitions for high-resolution-timer sleeps. */
+int torture_hrtimeout_ns(ktime_t baset_ns, u32 fuzzt_ns, struct torture_random_state *trsp);
+int torture_hrtimeout_us(u32 baset_us, u32 fuzzt_ns, struct torture_random_state *trsp);
+int torture_hrtimeout_ms(u32 baset_ms, u32 fuzzt_us, struct torture_random_state *trsp);
+int torture_hrtimeout_jiffies(u32 baset_j, struct torture_random_state *trsp);
+int torture_hrtimeout_s(u32 baset_s, u32 fuzzt_ms, struct torture_random_state *trsp);
+
/* Task shuffler, which causes CPUs to occasionally go idle. */
void torture_shuffle_task_register(struct task_struct *tp);
int torture_shuffle_init(long shuffint);
int register_vmap_purge_notifier(struct notifier_block *nb);
int unregister_vmap_purge_notifier(struct notifier_block *nb);
+#ifdef CONFIG_MMU
+bool vmalloc_dump_obj(void *object);
+#else
+static inline bool vmalloc_dump_obj(void *object) { return false; }
+#endif
+
#endif /* _LINUX_VMALLOC_H */
init_mm_internals();
+ rcu_init_tasks_generic();
do_pre_smp_initcalls();
lockup_detector_init();
#include <linux/moduleparam.h>
#include <linux/delay.h>
#include <linux/slab.h>
-#include <linux/percpu-rwsem.h>
#include <linux/torture.h>
#include <linux/reboot.h>
config TASKS_TRACE_RCU
def_bool 0
+ select IRQ_WORK
help
This option enables a task-based RCU implementation that uses
explicit rcu_read_lock_trace() read-side markers, and allows
config RCU_BOOST
bool "Enable RCU priority boosting"
- depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
- default n
+ depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT
+ default y if PREEMPT_RT
help
This option boosts the priority of preempted RCU readers that
block the current preemptible RCU grace period for too long.
smp_mb__after_unlock_lock(); \
} while (0)
-#define raw_spin_unlock_rcu_node(p) raw_spin_unlock(&ACCESS_PRIVATE(p, lock))
+#define raw_spin_unlock_rcu_node(p) \
+do { \
+ lockdep_assert_irqs_disabled(); \
+ raw_spin_unlock(&ACCESS_PRIVATE(p, lock)); \
+} while (0)
#define raw_spin_lock_irq_rcu_node(p) \
do { \
} while (0)
#define raw_spin_unlock_irq_rcu_node(p) \
- raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock))
+do { \
+ lockdep_assert_irqs_disabled(); \
+ raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock)); \
+} while (0)
#define raw_spin_lock_irqsave_rcu_node(p, flags) \
do { \
} while (0)
#define raw_spin_unlock_irqrestore_rcu_node(p, flags) \
- raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags)
+do { \
+ lockdep_assert_irqs_disabled(); \
+ raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags); \
+} while (0)
#define raw_spin_trylock_rcu_node(p) \
({ \
torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
torture_param(bool, gp_normal, false,
"Use normal (non-expedited) GP wait primitives");
+torture_param(bool, gp_poll, false, "Use polling GP wait primitives");
torture_param(bool, gp_sync, false, "Use synchronous GP wait primitives");
torture_param(int, irqreader, 1, "Allow RCU readers from irq handlers");
torture_param(int, leakpointer, 0, "Leak pointer dereferences from readers");
#define RCU_TORTURE_PIPE_LEN 10
+// Mailbox-like structure to check RCU global memory ordering.
+struct rcu_torture_reader_check {
+ unsigned long rtc_myloops;
+ int rtc_chkrdr;
+ unsigned long rtc_chkloops;
+ int rtc_ready;
+ struct rcu_torture_reader_check *rtc_assigner;
+} ____cacheline_internodealigned_in_smp;
+
+// Update-side data structure used to check RCU readers.
struct rcu_torture {
struct rcu_head rtort_rcu;
int rtort_pipe_count;
struct list_head rtort_free;
int rtort_mbtest;
+ struct rcu_torture_reader_check *rtort_chkp;
};
static LIST_HEAD(rcu_torture_freelist);
static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_count);
static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_batch);
static atomic_t rcu_torture_wcount[RCU_TORTURE_PIPE_LEN + 1];
+static struct rcu_torture_reader_check *rcu_torture_reader_mbchk;
static atomic_t n_rcu_torture_alloc;
static atomic_t n_rcu_torture_alloc_fail;
static atomic_t n_rcu_torture_free;
static atomic_t n_rcu_torture_mberror;
+static atomic_t n_rcu_torture_mbchk_fail;
+static atomic_t n_rcu_torture_mbchk_tries;
static atomic_t n_rcu_torture_error;
static long n_rcu_torture_barrier_error;
static long n_rcu_torture_boost_ktrerror;
#define RTWS_EXP_SYNC 4
#define RTWS_COND_GET 5
#define RTWS_COND_SYNC 6
-#define RTWS_SYNC 7
-#define RTWS_STUTTER 8
-#define RTWS_STOPPING 9
+#define RTWS_POLL_GET 7
+#define RTWS_POLL_WAIT 8
+#define RTWS_SYNC 9
+#define RTWS_STUTTER 10
+#define RTWS_STOPPING 11
static const char * const rcu_torture_writer_state_names[] = {
"RTWS_FIXED_DELAY",
"RTWS_DELAY",
"RTWS_EXP_SYNC",
"RTWS_COND_GET",
"RTWS_COND_SYNC",
+ "RTWS_POLL_GET",
+ "RTWS_POLL_WAIT",
"RTWS_SYNC",
"RTWS_STUTTER",
"RTWS_STOPPING",
void (*deferred_free)(struct rcu_torture *p);
void (*sync)(void);
void (*exp_sync)(void);
- unsigned long (*get_state)(void);
+ unsigned long (*get_gp_state)(void);
+ unsigned long (*start_gp_poll)(void);
+ bool (*poll_gp_state)(unsigned long oldstate);
void (*cond_sync)(unsigned long oldstate);
call_rcu_func_t call;
void (*cb_barrier)(void);
rcu_torture_pipe_update_one(struct rcu_torture *rp)
{
int i;
+ struct rcu_torture_reader_check *rtrcp = READ_ONCE(rp->rtort_chkp);
+ if (rtrcp) {
+ WRITE_ONCE(rp->rtort_chkp, NULL);
+ smp_store_release(&rtrcp->rtc_ready, 1); // Pair with smp_load_acquire().
+ }
i = READ_ONCE(rp->rtort_pipe_count);
if (i > RCU_TORTURE_PIPE_LEN)
i = RCU_TORTURE_PIPE_LEN;
.deferred_free = rcu_torture_deferred_free,
.sync = synchronize_rcu,
.exp_sync = synchronize_rcu_expedited,
- .get_state = get_state_synchronize_rcu,
+ .get_gp_state = get_state_synchronize_rcu,
.cond_sync = cond_synchronize_rcu,
.call = call_rcu,
.cb_barrier = rcu_barrier,
synchronize_srcu(srcu_ctlp);
}
+static unsigned long srcu_torture_get_gp_state(void)
+{
+ return get_state_synchronize_srcu(srcu_ctlp);
+}
+
+static unsigned long srcu_torture_start_gp_poll(void)
+{
+ return start_poll_synchronize_srcu(srcu_ctlp);
+}
+
+static bool srcu_torture_poll_gp_state(unsigned long oldstate)
+{
+ return poll_state_synchronize_srcu(srcu_ctlp, oldstate);
+}
+
static void srcu_torture_call(struct rcu_head *head,
rcu_callback_t func)
{
.deferred_free = srcu_torture_deferred_free,
.sync = srcu_torture_synchronize,
.exp_sync = srcu_torture_synchronize_expedited,
+ .get_gp_state = srcu_torture_get_gp_state,
+ .start_gp_poll = srcu_torture_start_gp_poll,
+ .poll_gp_state = srcu_torture_poll_gp_state,
.call = srcu_torture_call,
.cb_barrier = srcu_torture_barrier,
.stats = srcu_torture_stats,
return 0;
}
+// Used by writers to randomly choose from the available grace-period
+// primitives. The only purpose of the initialization is to size the array.
+static int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC, RTWS_COND_GET, RTWS_POLL_GET, RTWS_SYNC };
+static int nsynctypes;
+
/*
- * RCU torture writer kthread. Repeatedly substitutes a new structure
- * for that pointed to by rcu_torture_current, freeing the old structure
- * after a series of grace periods (the "pipeline").
+ * Determine which grace-period primitives are available.
*/
-static int
-rcu_torture_writer(void *arg)
+static void rcu_torture_write_types(void)
{
- bool can_expedite = !rcu_gp_is_expedited() && !rcu_gp_is_normal();
- int expediting = 0;
- unsigned long gp_snap;
bool gp_cond1 = gp_cond, gp_exp1 = gp_exp, gp_normal1 = gp_normal;
- bool gp_sync1 = gp_sync;
- int i;
- int oldnice = task_nice(current);
- struct rcu_torture *rp;
- struct rcu_torture *old_rp;
- static DEFINE_TORTURE_RANDOM(rand);
- bool stutter_waited;
- int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC,
- RTWS_COND_GET, RTWS_SYNC };
- int nsynctypes = 0;
-
- VERBOSE_TOROUT_STRING("rcu_torture_writer task started");
- if (!can_expedite)
- pr_alert("%s" TORTURE_FLAG
- " GP expediting controlled from boot/sysfs for %s.\n",
- torture_type, cur_ops->name);
+ bool gp_poll1 = gp_poll, gp_sync1 = gp_sync;
/* Initialize synctype[] array. If none set, take default. */
- if (!gp_cond1 && !gp_exp1 && !gp_normal1 && !gp_sync1)
- gp_cond1 = gp_exp1 = gp_normal1 = gp_sync1 = true;
- if (gp_cond1 && cur_ops->get_state && cur_ops->cond_sync) {
+ if (!gp_cond1 && !gp_exp1 && !gp_normal1 && !gp_poll1 && !gp_sync1)
+ gp_cond1 = gp_exp1 = gp_normal1 = gp_poll1 = gp_sync1 = true;
+ if (gp_cond1 && cur_ops->get_gp_state && cur_ops->cond_sync) {
synctype[nsynctypes++] = RTWS_COND_GET;
pr_info("%s: Testing conditional GPs.\n", __func__);
- } else if (gp_cond && (!cur_ops->get_state || !cur_ops->cond_sync)) {
+ } else if (gp_cond && (!cur_ops->get_gp_state || !cur_ops->cond_sync)) {
pr_alert("%s: gp_cond without primitives.\n", __func__);
}
if (gp_exp1 && cur_ops->exp_sync) {
} else if (gp_normal && !cur_ops->deferred_free) {
pr_alert("%s: gp_normal without primitives.\n", __func__);
}
+ if (gp_poll1 && cur_ops->start_gp_poll && cur_ops->poll_gp_state) {
+ synctype[nsynctypes++] = RTWS_POLL_GET;
+ pr_info("%s: Testing polling GPs.\n", __func__);
+ } else if (gp_poll && (!cur_ops->start_gp_poll || !cur_ops->poll_gp_state)) {
+ pr_alert("%s: gp_poll without primitives.\n", __func__);
+ }
if (gp_sync1 && cur_ops->sync) {
synctype[nsynctypes++] = RTWS_SYNC;
pr_info("%s: Testing normal GPs.\n", __func__);
} else if (gp_sync && !cur_ops->sync) {
pr_alert("%s: gp_sync without primitives.\n", __func__);
}
+}
+
+/*
+ * RCU torture writer kthread. Repeatedly substitutes a new structure
+ * for that pointed to by rcu_torture_current, freeing the old structure
+ * after a series of grace periods (the "pipeline").
+ */
+static int
+rcu_torture_writer(void *arg)
+{
+ bool boot_ended;
+ bool can_expedite = !rcu_gp_is_expedited() && !rcu_gp_is_normal();
+ unsigned long cookie;
+ int expediting = 0;
+ unsigned long gp_snap;
+ int i;
+ int idx;
+ int oldnice = task_nice(current);
+ struct rcu_torture *rp;
+ struct rcu_torture *old_rp;
+ static DEFINE_TORTURE_RANDOM(rand);
+ bool stutter_waited;
+
+ VERBOSE_TOROUT_STRING("rcu_torture_writer task started");
+ if (!can_expedite)
+ pr_alert("%s" TORTURE_FLAG
+ " GP expediting controlled from boot/sysfs for %s.\n",
+ torture_type, cur_ops->name);
if (WARN_ONCE(nsynctypes == 0,
"rcu_torture_writer: No update-side primitives.\n")) {
/*
do {
rcu_torture_writer_state = RTWS_FIXED_DELAY;
- schedule_timeout_uninterruptible(1);
+ torture_hrtimeout_us(500, 1000, &rand);
rp = rcu_torture_alloc();
if (rp == NULL)
continue;
atomic_inc(&rcu_torture_wcount[i]);
WRITE_ONCE(old_rp->rtort_pipe_count,
old_rp->rtort_pipe_count + 1);
+ if (cur_ops->get_gp_state && cur_ops->poll_gp_state) {
+ idx = cur_ops->readlock();
+ cookie = cur_ops->get_gp_state();
+ WARN_ONCE(rcu_torture_writer_state != RTWS_DEF_FREE &&
+ cur_ops->poll_gp_state(cookie),
+ "%s: Cookie check 1 failed %s(%d) %lu->%lu\n",
+ __func__,
+ rcu_torture_writer_state_getname(),
+ rcu_torture_writer_state,
+ cookie, cur_ops->get_gp_state());
+ cur_ops->readunlock(idx);
+ }
switch (synctype[torture_random(&rand) % nsynctypes]) {
case RTWS_DEF_FREE:
rcu_torture_writer_state = RTWS_DEF_FREE;
break;
case RTWS_COND_GET:
rcu_torture_writer_state = RTWS_COND_GET;
- gp_snap = cur_ops->get_state();
- i = torture_random(&rand) % 16;
- if (i != 0)
- schedule_timeout_interruptible(i);
- udelay(torture_random(&rand) % 1000);
+ gp_snap = cur_ops->get_gp_state();
+ torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
rcu_torture_writer_state = RTWS_COND_SYNC;
cur_ops->cond_sync(gp_snap);
rcu_torture_pipe_update(old_rp);
break;
+ case RTWS_POLL_GET:
+ rcu_torture_writer_state = RTWS_POLL_GET;
+ gp_snap = cur_ops->start_gp_poll();
+ rcu_torture_writer_state = RTWS_POLL_WAIT;
+ while (!cur_ops->poll_gp_state(gp_snap))
+ torture_hrtimeout_jiffies(torture_random(&rand) % 16,
+ &rand);
+ rcu_torture_pipe_update(old_rp);
+ break;
case RTWS_SYNC:
rcu_torture_writer_state = RTWS_SYNC;
cur_ops->sync();
WARN_ON_ONCE(1);
break;
}
+ if (cur_ops->get_gp_state && cur_ops->poll_gp_state)
+ WARN_ONCE(rcu_torture_writer_state != RTWS_DEF_FREE &&
+ !cur_ops->poll_gp_state(cookie),
+ "%s: Cookie check 2 failed %s(%d) %lu->%lu\n",
+ __func__,
+ rcu_torture_writer_state_getname(),
+ rcu_torture_writer_state,
+ cookie, cur_ops->get_gp_state());
}
WRITE_ONCE(rcu_torture_current_version,
rcu_torture_current_version + 1);
!rcu_gp_is_normal();
}
rcu_torture_writer_state = RTWS_STUTTER;
+ boot_ended = rcu_inkernel_boot_has_ended();
stutter_waited = stutter_wait("rcu_torture_writer");
if (stutter_waited &&
!READ_ONCE(rcu_fwd_cb_nodelay) &&
!cur_ops->slow_gps &&
!torture_must_stop() &&
- rcu_inkernel_boot_has_ended())
+ boot_ended)
for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++)
if (list_empty(&rcu_tortures[i].rtort_free) &&
rcu_access_pointer(rcu_torture_current) !=
static int
rcu_torture_fakewriter(void *arg)
{
+ unsigned long gp_snap;
DEFINE_TORTURE_RANDOM(rand);
VERBOSE_TOROUT_STRING("rcu_torture_fakewriter task started");
set_user_nice(current, MAX_NICE);
do {
- schedule_timeout_uninterruptible(1 + torture_random(&rand)%10);
- udelay(torture_random(&rand) & 0x3ff);
+ torture_hrtimeout_jiffies(torture_random(&rand) % 10, &rand);
if (cur_ops->cb_barrier != NULL &&
torture_random(&rand) % (nfakewriters * 8) == 0) {
cur_ops->cb_barrier();
- } else if (gp_normal == gp_exp) {
- if (cur_ops->sync && torture_random(&rand) & 0x80)
- cur_ops->sync();
- else if (cur_ops->exp_sync)
+ } else {
+ switch (synctype[torture_random(&rand) % nsynctypes]) {
+ case RTWS_DEF_FREE:
+ break;
+ case RTWS_EXP_SYNC:
cur_ops->exp_sync();
- } else if (gp_normal && cur_ops->sync) {
- cur_ops->sync();
- } else if (cur_ops->exp_sync) {
- cur_ops->exp_sync();
+ break;
+ case RTWS_COND_GET:
+ gp_snap = cur_ops->get_gp_state();
+ torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
+ cur_ops->cond_sync(gp_snap);
+ break;
+ case RTWS_POLL_GET:
+ gp_snap = cur_ops->start_gp_poll();
+ while (!cur_ops->poll_gp_state(gp_snap)) {
+ torture_hrtimeout_jiffies(torture_random(&rand) % 16,
+ &rand);
+ }
+ break;
+ case RTWS_SYNC:
+ cur_ops->sync();
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ break;
+ }
}
stutter_wait("rcu_torture_fakewriter");
} while (!torture_must_stop());
kfree(rhp);
}
+// Set up and carry out testing of RCU's global memory ordering
+static void rcu_torture_reader_do_mbchk(long myid, struct rcu_torture *rtp,
+ struct torture_random_state *trsp)
+{
+ unsigned long loops;
+ int noc = torture_num_online_cpus();
+ int rdrchked;
+ int rdrchker;
+ struct rcu_torture_reader_check *rtrcp; // Me.
+ struct rcu_torture_reader_check *rtrcp_assigner; // Assigned us to do checking.
+ struct rcu_torture_reader_check *rtrcp_chked; // Reader being checked.
+ struct rcu_torture_reader_check *rtrcp_chker; // Reader doing checking when not me.
+
+ if (myid < 0)
+ return; // Don't try this from timer handlers.
+
+ // Increment my counter.
+ rtrcp = &rcu_torture_reader_mbchk[myid];
+ WRITE_ONCE(rtrcp->rtc_myloops, rtrcp->rtc_myloops + 1);
+
+ // Attempt to assign someone else some checking work.
+ rdrchked = torture_random(trsp) % nrealreaders;
+ rtrcp_chked = &rcu_torture_reader_mbchk[rdrchked];
+ rdrchker = torture_random(trsp) % nrealreaders;
+ rtrcp_chker = &rcu_torture_reader_mbchk[rdrchker];
+ if (rdrchked != myid && rdrchked != rdrchker && noc >= rdrchked && noc >= rdrchker &&
+ smp_load_acquire(&rtrcp->rtc_chkrdr) < 0 && // Pairs with smp_store_release below.
+ !READ_ONCE(rtp->rtort_chkp) &&
+ !smp_load_acquire(&rtrcp_chker->rtc_assigner)) { // Pairs with smp_store_release below.
+ rtrcp->rtc_chkloops = READ_ONCE(rtrcp_chked->rtc_myloops);
+ WARN_ON_ONCE(rtrcp->rtc_chkrdr >= 0);
+ rtrcp->rtc_chkrdr = rdrchked;
+ WARN_ON_ONCE(rtrcp->rtc_ready); // This gets set after the grace period ends.
+ if (cmpxchg_relaxed(&rtrcp_chker->rtc_assigner, NULL, rtrcp) ||
+ cmpxchg_relaxed(&rtp->rtort_chkp, NULL, rtrcp))
+ (void)cmpxchg_relaxed(&rtrcp_chker->rtc_assigner, rtrcp, NULL); // Back out.
+ }
+
+ // If assigned some completed work, do it!
+ rtrcp_assigner = READ_ONCE(rtrcp->rtc_assigner);
+ if (!rtrcp_assigner || !smp_load_acquire(&rtrcp_assigner->rtc_ready))
+ return; // No work or work not yet ready.
+ rdrchked = rtrcp_assigner->rtc_chkrdr;
+ if (WARN_ON_ONCE(rdrchked < 0))
+ return;
+ rtrcp_chked = &rcu_torture_reader_mbchk[rdrchked];
+ loops = READ_ONCE(rtrcp_chked->rtc_myloops);
+ atomic_inc(&n_rcu_torture_mbchk_tries);
+ if (ULONG_CMP_LT(loops, rtrcp_assigner->rtc_chkloops))
+ atomic_inc(&n_rcu_torture_mbchk_fail);
+ rtrcp_assigner->rtc_chkloops = loops + ULONG_MAX / 2;
+ rtrcp_assigner->rtc_ready = 0;
+ smp_store_release(&rtrcp->rtc_assigner, NULL); // Someone else can assign us work.
+ smp_store_release(&rtrcp_assigner->rtc_chkrdr, -1); // Assigner can again assign.
+}
+
/*
* Do one extension of an RCU read-side critical section using the
* current reader state in readstate (set to zero for initial entry
* no data to read. Can be invoked both from process context and
* from a timer handler.
*/
-static bool rcu_torture_one_read(struct torture_random_state *trsp)
+static bool rcu_torture_one_read(struct torture_random_state *trsp, long myid)
{
+ unsigned long cookie;
int i;
unsigned long started;
unsigned long completed;
WARN_ON_ONCE(!rcu_is_watching());
newstate = rcutorture_extend_mask(readstate, trsp);
rcutorture_one_extend(&readstate, newstate, trsp, rtrsp++);
+ if (cur_ops->get_gp_state && cur_ops->poll_gp_state)
+ cookie = cur_ops->get_gp_state();
started = cur_ops->get_gp_seq();
ts = rcu_trace_clock_local();
p = rcu_dereference_check(rcu_torture_current,
}
if (p->rtort_mbtest == 0)
atomic_inc(&n_rcu_torture_mberror);
+ rcu_torture_reader_do_mbchk(myid, p, trsp);
rtrsp = rcutorture_loop_extend(&readstate, trsp, rtrsp);
preempt_disable();
pipe_count = READ_ONCE(p->rtort_pipe_count);
}
__this_cpu_inc(rcu_torture_batch[completed]);
preempt_enable();
+ if (cur_ops->get_gp_state && cur_ops->poll_gp_state)
+ WARN_ONCE(cur_ops->poll_gp_state(cookie),
+ "%s: Cookie check 3 failed %s(%d) %lu->%lu\n",
+ __func__,
+ rcu_torture_writer_state_getname(),
+ rcu_torture_writer_state,
+ cookie, cur_ops->get_gp_state());
rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
WARN_ON_ONCE(readstate & RCUTORTURE_RDR_MASK);
// This next splat is expected behavior if leakpointer, especially
static void rcu_torture_timer(struct timer_list *unused)
{
atomic_long_inc(&n_rcu_torture_timers);
- (void)rcu_torture_one_read(this_cpu_ptr(&rcu_torture_timer_rand));
+ (void)rcu_torture_one_read(this_cpu_ptr(&rcu_torture_timer_rand), -1);
/* Test call_rcu() invocation from interrupt handler. */
if (cur_ops->call) {
if (!timer_pending(&t))
mod_timer(&t, jiffies + 1);
}
- if (!rcu_torture_one_read(&rand) && !torture_must_stop())
+ if (!rcu_torture_one_read(&rand, myid) && !torture_must_stop())
schedule_timeout_interruptible(HZ);
if (time_after(jiffies, lastsleep) && !torture_must_stop()) {
- schedule_timeout_interruptible(1);
+ torture_hrtimeout_us(500, 1000, &rand);
lastsleep = jiffies + 10;
}
- while (num_online_cpus() < mynumonline && !torture_must_stop())
+ while (torture_num_online_cpus() < mynumonline && !torture_must_stop())
schedule_timeout_interruptible(HZ / 5);
stutter_wait("rcu_torture_reader");
} while (!torture_must_stop());
atomic_read(&n_rcu_torture_alloc),
atomic_read(&n_rcu_torture_alloc_fail),
atomic_read(&n_rcu_torture_free));
- pr_cont("rtmbe: %d rtbe: %ld rtbke: %ld rtbre: %ld ",
+ pr_cont("rtmbe: %d rtmbkf: %d/%d rtbe: %ld rtbke: %ld rtbre: %ld ",
atomic_read(&n_rcu_torture_mberror),
+ atomic_read(&n_rcu_torture_mbchk_fail), atomic_read(&n_rcu_torture_mbchk_tries),
n_rcu_torture_barrier_error,
n_rcu_torture_boost_ktrerror,
n_rcu_torture_boost_rterror);
pr_alert("%s%s ", torture_type, TORTURE_FLAG);
if (atomic_read(&n_rcu_torture_mberror) ||
+ atomic_read(&n_rcu_torture_mbchk_fail) ||
n_rcu_torture_barrier_error || n_rcu_torture_boost_ktrerror ||
n_rcu_torture_boost_rterror || n_rcu_torture_boost_failure ||
i > 1) {
pr_cont("%s", "!!! ");
atomic_inc(&n_rcu_torture_error);
WARN_ON_ONCE(atomic_read(&n_rcu_torture_mberror));
+ WARN_ON_ONCE(atomic_read(&n_rcu_torture_mbchk_fail));
WARN_ON_ONCE(n_rcu_torture_barrier_error); // rcu_barrier()
WARN_ON_ONCE(n_rcu_torture_boost_ktrerror); // no boost kthread
WARN_ON_ONCE(n_rcu_torture_boost_rterror); // can't set RT prio
// Minimize time between reading and exiting.
while (!kthread_should_stop())
schedule_timeout_uninterruptible(1);
- (void)rcu_torture_one_read(trsp);
+ (void)rcu_torture_one_read(trsp, -1);
return 0;
}
kfree(reader_tasks);
reader_tasks = NULL;
}
+ kfree(rcu_torture_reader_mbchk);
+ rcu_torture_reader_mbchk = NULL;
if (fakewriter_tasks) {
for (i = 0; i < nfakewriters; i++)
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
struct rcu_head rh1;
struct rcu_head rh2;
+ struct rcu_head *rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
init_rcu_head_on_stack(&rh1);
init_rcu_head_on_stack(&rh2);
local_irq_disable(); /* Make it harder to start a new grace period. */
call_rcu(&rh2, rcu_torture_leak_cb);
call_rcu(&rh2, rcu_torture_err_cb); /* Duplicate callback. */
+ if (rhp) {
+ call_rcu(rhp, rcu_torture_leak_cb);
+ call_rcu(rhp, rcu_torture_err_cb); /* Another duplicate callback. */
+ }
local_irq_enable();
rcu_read_unlock();
preempt_enable();
atomic_set(&n_rcu_torture_alloc_fail, 0);
atomic_set(&n_rcu_torture_free, 0);
atomic_set(&n_rcu_torture_mberror, 0);
+ atomic_set(&n_rcu_torture_mbchk_fail, 0);
+ atomic_set(&n_rcu_torture_mbchk_tries, 0);
atomic_set(&n_rcu_torture_error, 0);
n_rcu_torture_barrier_error = 0;
n_rcu_torture_boost_ktrerror = 0;
/* Start up the kthreads. */
+ rcu_torture_write_types();
firsterr = torture_create_kthread(rcu_torture_writer, NULL,
writer_task);
if (firsterr)
}
reader_tasks = kcalloc(nrealreaders, sizeof(reader_tasks[0]),
GFP_KERNEL);
- if (reader_tasks == NULL) {
+ rcu_torture_reader_mbchk = kcalloc(nrealreaders, sizeof(*rcu_torture_reader_mbchk),
+ GFP_KERNEL);
+ if (!reader_tasks || !rcu_torture_reader_mbchk) {
VERBOSE_TOROUT_ERRSTRING("out of memory");
firsterr = -ENOMEM;
goto unwind;
}
for (i = 0; i < nrealreaders; i++) {
+ rcu_torture_reader_mbchk[i].rtc_chkrdr = -1;
firsterr = torture_create_kthread(rcu_torture_reader, (void *)i,
reader_tasks[i]);
if (firsterr)
#define VERBOSE_SCALEOUT(s, x...) \
do { if (verbose) pr_alert("%s" SCALE_FLAG s, scale_type, ## x); } while (0)
+static atomic_t verbose_batch_ctr;
+
+#define VERBOSE_SCALEOUT_BATCH(s, x...) \
+do { \
+ if (verbose && \
+ (verbose_batched <= 0 || \
+ !(atomic_inc_return(&verbose_batch_ctr) % verbose_batched))) { \
+ schedule_timeout_uninterruptible(1); \
+ pr_alert("%s" SCALE_FLAG s, scale_type, ## x); \
+ } \
+} while (0)
+
#define VERBOSE_SCALEOUT_ERRSTRING(s, x...) \
do { if (verbose) pr_alert("%s" SCALE_FLAG "!!! " s, scale_type, ## x); } while (0)
MODULE_PARM_DESC(scale_type, "Type of test (rcu, srcu, refcnt, rwsem, rwlock.");
torture_param(int, verbose, 0, "Enable verbose debugging printk()s");
+torture_param(int, verbose_batched, 0, "Batch verbose debugging printk()s");
// Wait until there are multiple CPUs before starting test.
torture_param(int, holdoff, IS_BUILTIN(CONFIG_RCU_REF_SCALE_TEST) ? 10 : 0,
u64 start;
s64 duration;
- VERBOSE_SCALEOUT("ref_scale_reader %ld: task started", me);
+ VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: task started", me);
set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
set_user_nice(current, MAX_NICE);
atomic_inc(&n_init);
if (holdoff)
schedule_timeout_interruptible(holdoff * HZ);
repeat:
- VERBOSE_SCALEOUT("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, smp_processor_id());
+ VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, smp_processor_id());
// Wait for signal that this reader can start.
wait_event(rt->wq, (atomic_read(&nreaders_exp) && smp_load_acquire(&rt->start_reader)) ||
while (atomic_read_acquire(&n_started))
cpu_relax();
- VERBOSE_SCALEOUT("ref_scale_reader %ld: experiment %d started", me, exp_idx);
+ VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: experiment %d started", me, exp_idx);
// To reduce noise, do an initial cache-warming invocation, check
if (atomic_dec_and_test(&nreaders_exp))
wake_up(&main_wq);
- VERBOSE_SCALEOUT("ref_scale_reader %ld: experiment %d ended, (readers remaining=%d)",
- me, exp_idx, atomic_read(&nreaders_exp));
+ VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: experiment %d ended, (readers remaining=%d)",
+ me, exp_idx, atomic_read(&nreaders_exp));
if (!torture_must_stop())
goto repeat;
ssp->srcu_gp_running = false;
ssp->srcu_gp_waiting = false;
ssp->srcu_idx = 0;
+ ssp->srcu_idx_max = 0;
INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
INIT_LIST_HEAD(&ssp->srcu_work.entry);
return 0;
WARN_ON(ssp->srcu_gp_waiting);
WARN_ON(ssp->srcu_cb_head);
WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
+ WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max);
+ WARN_ON(ssp->srcu_idx & 0x1);
}
EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
struct srcu_struct *ssp;
ssp = container_of(wp, struct srcu_struct, srcu_work);
- if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head))
+ if (ssp->srcu_gp_running || USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
return; /* Already running or nothing to do. */
/* Remove recently arrived callbacks and wait for readers. */
ssp->srcu_cb_head = NULL;
ssp->srcu_cb_tail = &ssp->srcu_cb_head;
local_irq_enable();
- idx = ssp->srcu_idx;
- WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx);
+ idx = (ssp->srcu_idx & 0x2) / 2;
+ WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */
swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
+ WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
/* Invoke the callbacks we removed above. */
while (lh) {
* straighten that out.
*/
WRITE_ONCE(ssp->srcu_gp_running, false);
- if (READ_ONCE(ssp->srcu_cb_head))
+ if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
schedule_work(&ssp->srcu_work);
}
EXPORT_SYMBOL_GPL(srcu_drive_gp);
+static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
+{
+ unsigned short cookie;
+
+ cookie = get_state_synchronize_srcu(ssp);
+ if (USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie))
+ return;
+ WRITE_ONCE(ssp->srcu_idx_max, cookie);
+ if (!READ_ONCE(ssp->srcu_gp_running)) {
+ if (likely(srcu_init_done))
+ schedule_work(&ssp->srcu_work);
+ else if (list_empty(&ssp->srcu_work.entry))
+ list_add(&ssp->srcu_work.entry, &srcu_boot_list);
+ }
+}
+
/*
* Enqueue an SRCU callback on the specified srcu_struct structure,
* initiating grace-period processing if it is not already running.
*ssp->srcu_cb_tail = rhp;
ssp->srcu_cb_tail = &rhp->next;
local_irq_restore(flags);
- if (!READ_ONCE(ssp->srcu_gp_running)) {
- if (likely(srcu_init_done))
- schedule_work(&ssp->srcu_work);
- else if (list_empty(&ssp->srcu_work.entry))
- list_add(&ssp->srcu_work.entry, &srcu_boot_list);
- }
+ srcu_gp_start_if_needed(ssp);
}
EXPORT_SYMBOL_GPL(call_srcu);
}
EXPORT_SYMBOL_GPL(synchronize_srcu);
+/*
+ * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
+ */
+unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
+{
+ unsigned long ret;
+
+ barrier();
+ ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1;
+ barrier();
+ return ret & USHRT_MAX;
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
+
+/*
+ * start_poll_synchronize_srcu - Provide cookie and start grace period
+ *
+ * The difference between this and get_state_synchronize_srcu() is that
+ * this function ensures that the poll_state_synchronize_srcu() will
+ * eventually return the value true.
+ */
+unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
+{
+ unsigned long ret = get_state_synchronize_srcu(ssp);
+
+ srcu_gp_start_if_needed(ssp);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
+
+/*
+ * poll_state_synchronize_srcu - Has cookie's grace period ended?
+ */
+bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
+{
+ bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie);
+
+ barrier();
+ return ret;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
+
/* Lockdep diagnostics. */
void __init rcu_scheduler_starting(void)
{
{
}
+/*
+ * Start an SRCU grace period, and also queue the callback if non-NULL.
+ */
+static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
+ struct rcu_head *rhp, bool do_norm)
+{
+ unsigned long flags;
+ int idx;
+ bool needexp = false;
+ bool needgp = false;
+ unsigned long s;
+ struct srcu_data *sdp;
+
+ check_init_srcu_struct(ssp);
+ idx = srcu_read_lock(ssp);
+ sdp = raw_cpu_ptr(ssp->sda);
+ spin_lock_irqsave_rcu_node(sdp, flags);
+ if (rhp)
+ rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
+ rcu_segcblist_advance(&sdp->srcu_cblist,
+ rcu_seq_current(&ssp->srcu_gp_seq));
+ s = rcu_seq_snap(&ssp->srcu_gp_seq);
+ (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
+ if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
+ sdp->srcu_gp_seq_needed = s;
+ needgp = true;
+ }
+ if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
+ sdp->srcu_gp_seq_needed_exp = s;
+ needexp = true;
+ }
+ spin_unlock_irqrestore_rcu_node(sdp, flags);
+ if (needgp)
+ srcu_funnel_gp_start(ssp, sdp, s, do_norm);
+ else if (needexp)
+ srcu_funnel_exp_start(ssp, sdp->mynode, s);
+ srcu_read_unlock(ssp, idx);
+ return s;
+}
+
/*
* Enqueue an SRCU callback on the srcu_data structure associated with
* the current CPU and the specified srcu_struct structure, initiating
static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
rcu_callback_t func, bool do_norm)
{
- unsigned long flags;
- int idx;
- bool needexp = false;
- bool needgp = false;
- unsigned long s;
- struct srcu_data *sdp;
-
- check_init_srcu_struct(ssp);
if (debug_rcu_head_queue(rhp)) {
/* Probable double call_srcu(), so leak the callback. */
WRITE_ONCE(rhp->func, srcu_leak_callback);
return;
}
rhp->func = func;
- idx = srcu_read_lock(ssp);
- sdp = raw_cpu_ptr(ssp->sda);
- spin_lock_irqsave_rcu_node(sdp, flags);
- rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
- rcu_segcblist_advance(&sdp->srcu_cblist,
- rcu_seq_current(&ssp->srcu_gp_seq));
- s = rcu_seq_snap(&ssp->srcu_gp_seq);
- (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
- if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
- sdp->srcu_gp_seq_needed = s;
- needgp = true;
- }
- if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
- sdp->srcu_gp_seq_needed_exp = s;
- needexp = true;
- }
- spin_unlock_irqrestore_rcu_node(sdp, flags);
- if (needgp)
- srcu_funnel_gp_start(ssp, sdp, s, do_norm);
- else if (needexp)
- srcu_funnel_exp_start(ssp, sdp->mynode, s);
- srcu_read_unlock(ssp, idx);
+ (void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
}
/**
}
EXPORT_SYMBOL_GPL(synchronize_srcu);
+/**
+ * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
+ * @ssp: srcu_struct to provide cookie for.
+ *
+ * This function returns a cookie that can be passed to
+ * poll_state_synchronize_srcu(), which will return true if a full grace
+ * period has elapsed in the meantime. It is the caller's responsibility
+ * to make sure that grace period happens, for example, by invoking
+ * call_srcu() after return from get_state_synchronize_srcu().
+ */
+unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
+{
+ // Any prior manipulation of SRCU-protected data must happen
+ // before the load from ->srcu_gp_seq.
+ smp_mb();
+ return rcu_seq_snap(&ssp->srcu_gp_seq);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
+
+/**
+ * start_poll_synchronize_srcu - Provide cookie and start grace period
+ * @ssp: srcu_struct to provide cookie for.
+ *
+ * This function returns a cookie that can be passed to
+ * poll_state_synchronize_srcu(), which will return true if a full grace
+ * period has elapsed in the meantime. Unlike get_state_synchronize_srcu(),
+ * this function also ensures that any needed SRCU grace period will be
+ * started. This convenience does come at a cost in terms of CPU overhead.
+ */
+unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
+{
+ return srcu_gp_start_if_needed(ssp, NULL, true);
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
+
+/**
+ * poll_state_synchronize_srcu - Has cookie's grace period ended?
+ * @ssp: srcu_struct to provide cookie for.
+ * @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu().
+ *
+ * This function takes the cookie that was returned from either
+ * get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and
+ * returns @true if an SRCU grace period elapsed since the time that the
+ * cookie was created.
+ *
+ * Because cookies are finite in size, wrapping/overflow is possible.
+ * This is more pronounced on 32-bit systems where cookies are 32 bits,
+ * where in theory wrapping could happen in about 14 hours assuming
+ * 25-microsecond expedited SRCU grace periods. However, a more likely
+ * overflow lower bound is on the order of 24 days in the case of
+ * one-millisecond SRCU grace periods. Of course, wrapping in a 64-bit
+ * system requires geologic timespans, as in more than seven million years
+ * even for expedited SRCU grace periods.
+ *
+ * Wrapping/overflow is much more of an issue for CONFIG_SMP=n systems
+ * that also have CONFIG_PREEMPTION=n, which selects Tiny SRCU. This uses
+ * a 16-bit cookie, which rcutorture routinely wraps in a matter of a
+ * few minutes. If this proves to be a problem, this counter will be
+ * expanded to the same size as for Tree SRCU.
+ */
+bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
+{
+ if (!rcu_seq_done(&ssp->srcu_gp_seq, cookie))
+ return false;
+ // Ensure that the end of the SRCU grace period happens before
+ // any subsequent code that the caller might execute.
+ smp_mb(); // ^^^
+ return true;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
+
/*
* Callback function for srcu_barrier() use.
*/
}
}
-/* Spawn RCU-tasks grace-period kthread, e.g., at core_initcall() time. */
+/* Spawn RCU-tasks grace-period kthread. */
static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp)
{
struct task_struct *t;
rcu_spawn_tasks_kthread_generic(&rcu_tasks);
return 0;
}
-core_initcall(rcu_spawn_tasks_kthread);
#if !defined(CONFIG_TINY_RCU)
void show_rcu_tasks_classic_gp_kthread(void)
rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude);
return 0;
}
-core_initcall(rcu_spawn_tasks_rude_kthread);
#if !defined(CONFIG_TINY_RCU)
void show_rcu_tasks_rude_gp_kthread(void)
static void rcu_tasks_trace_pertask(struct task_struct *t,
struct list_head *hop)
{
+ // During early boot when there is only the one boot CPU, there
+ // is no idle task for the other CPUs. Just return.
+ if (unlikely(t == NULL))
+ return;
+
WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
WRITE_ONCE(t->trc_reader_checked, false);
t->trc_ipi_to_cpu = -1;
rcu_spawn_tasks_kthread_generic(&rcu_tasks_trace);
return 0;
}
-core_initcall(rcu_spawn_tasks_trace_kthread);
#if !defined(CONFIG_TINY_RCU)
void show_rcu_tasks_trace_gp_kthread(void)
}
#endif /* #ifndef CONFIG_TINY_RCU */
+#ifdef CONFIG_PROVE_RCU
+struct rcu_tasks_test_desc {
+ struct rcu_head rh;
+ const char *name;
+ bool notrun;
+};
+
+static struct rcu_tasks_test_desc tests[] = {
+ {
+ .name = "call_rcu_tasks()",
+ /* If not defined, the test is skipped. */
+ .notrun = !IS_ENABLED(CONFIG_TASKS_RCU),
+ },
+ {
+ .name = "call_rcu_tasks_rude()",
+ /* If not defined, the test is skipped. */
+ .notrun = !IS_ENABLED(CONFIG_TASKS_RUDE_RCU),
+ },
+ {
+ .name = "call_rcu_tasks_trace()",
+ /* If not defined, the test is skipped. */
+ .notrun = !IS_ENABLED(CONFIG_TASKS_TRACE_RCU)
+ }
+};
+
+static void test_rcu_tasks_callback(struct rcu_head *rhp)
+{
+ struct rcu_tasks_test_desc *rttd =
+ container_of(rhp, struct rcu_tasks_test_desc, rh);
+
+ pr_info("Callback from %s invoked.\n", rttd->name);
+
+ rttd->notrun = true;
+}
+
+static void rcu_tasks_initiate_self_tests(void)
+{
+ pr_info("Running RCU-tasks wait API self tests\n");
+#ifdef CONFIG_TASKS_RCU
+ synchronize_rcu_tasks();
+ call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
+#endif
+
+#ifdef CONFIG_TASKS_RUDE_RCU
+ synchronize_rcu_tasks_rude();
+ call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
+#endif
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+ synchronize_rcu_tasks_trace();
+ call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
+#endif
+}
+
+static int rcu_tasks_verify_self_tests(void)
+{
+ int ret = 0;
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(tests); i++) {
+ if (!tests[i].notrun) { // still hanging.
+ pr_err("%s has been failed.\n", tests[i].name);
+ ret = -1;
+ }
+ }
+
+ if (ret)
+ WARN_ON(1);
+
+ return ret;
+}
+late_initcall(rcu_tasks_verify_self_tests);
+#else /* #ifdef CONFIG_PROVE_RCU */
+static void rcu_tasks_initiate_self_tests(void) { }
+#endif /* #else #ifdef CONFIG_PROVE_RCU */
+
+void __init rcu_init_tasks_generic(void)
+{
+#ifdef CONFIG_TASKS_RCU
+ rcu_spawn_tasks_kthread();
+#endif
+
+#ifdef CONFIG_TASKS_RUDE_RCU
+ rcu_spawn_tasks_rude_kthread();
+#endif
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+ rcu_spawn_tasks_trace_kthread();
+#endif
+
+ // Run the self-tests.
+ rcu_tasks_initiate_self_tests();
+}
+
#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
static inline void rcu_tasks_bootup_oddness(void) {}
void show_rcu_tasks_gp_kthreads(void) {}
static bool dump_tree;
module_param(dump_tree, bool, 0444);
/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
-static bool use_softirq = true;
+static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);
+#ifndef CONFIG_PREEMPT_RT
module_param(use_softirq, bool, 0444);
+#endif
/* Control rcu_node-tree auto-balancing at boot time. */
static bool rcu_fanout_exact;
module_param(rcu_fanout_exact, bool, 0444);
* go offline later. Please also refer to "Hotplug CPU" section
* of RCU's Requirements documentation.
*/
- rcu_state.gp_state = RCU_GP_ONOFF;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
rcu_for_each_leaf_node(rnp) {
smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values.
firstseq = READ_ONCE(rnp->ofl_seq);
* The grace period cannot complete until the initialization
* process finishes, because this kthread handles both.
*/
- rcu_state.gp_state = RCU_GP_INIT;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT);
rcu_for_each_node_breadth_first(rnp) {
rcu_gp_slow(gp_init_delay);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
ret = 0;
for (;;) {
if (!ret) {
- rcu_state.jiffies_force_qs = jiffies + j;
+ WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j);
+ /*
+ * jiffies_force_qs before RCU_GP_WAIT_FQS state
+ * update; required for stall checks.
+ */
+ smp_wmb();
WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
jiffies + (j ? 3 * j : 2));
}
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("fqswait"));
- rcu_state.gp_state = RCU_GP_WAIT_FQS;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
ret = swait_event_idle_timeout_exclusive(
rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);
rcu_gp_torture_wait();
- rcu_state.gp_state = RCU_GP_DOING_FQS;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
/* Locking provides needed memory barriers. */
/* If grace period done, leave loop. */
if (!READ_ONCE(rnp->qsmask) &&
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
rcu_seq_end(&rcu_state.gp_seq);
ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
- rcu_state.gp_state = RCU_GP_IDLE;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE);
/* Check for GP requests since above loop. */
rdp = this_cpu_ptr(&rcu_data);
if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
for (;;) {
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("reqwait"));
- rcu_state.gp_state = RCU_GP_WAIT_GPS;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS);
swait_event_idle_exclusive(rcu_state.gp_wq,
READ_ONCE(rcu_state.gp_flags) &
RCU_GP_FLAG_INIT);
rcu_gp_torture_wait();
- rcu_state.gp_state = RCU_GP_DONE_GPS;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS);
/* Locking provides needed memory barrier. */
if (rcu_gp_init())
break;
rcu_gp_fqs_loop();
/* Handle grace-period end. */
- rcu_state.gp_state = RCU_GP_CLEANUP;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP);
rcu_gp_cleanup();
- rcu_state.gp_state = RCU_GP_CLEANED;
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED);
}
}
void rcu_sched_clock_irq(int user)
{
trace_rcu_utilization(TPS("Start scheduler-tick"));
+ lockdep_assert_irqs_disabled();
raw_cpu_inc(rcu_data.ticks_this_gp);
/* The load-acquire pairs with the store-release setting to true. */
if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
rcu_flavor_sched_clock_irq(user);
if (rcu_pending(user))
invoke_rcu_core();
+ lockdep_assert_irqs_disabled();
trace_rcu_utilization(TPS("End scheduler-tick"));
}
static void
__call_rcu(struct rcu_head *head, rcu_callback_t func)
{
+ static atomic_t doublefrees;
unsigned long flags;
struct rcu_data *rdp;
bool was_alldone;
* Use rcu:rcu_callback trace event to find the previous
* time callback was passed to __call_rcu().
*/
- WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pS()!!!\n",
- head, head->func);
+ if (atomic_inc_return(&doublefrees) < 4) {
+ pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
+ mem_dump_obj(head);
+ }
WRITE_ONCE(head->func, rcu_leak_callback);
return;
}
goto unlock_return;
}
+ kasan_record_aux_stack(ptr);
success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr);
if (!success) {
run_page_cache_worker(krcp);
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
+ lockdep_assert_irqs_disabled();
+
/* Check for CPU stalls, if enabled. */
check_cpu_stall(rdp);
data_race(rnp_root->expmask),
".T"[!!data_race(rnp_root->exp_tasks)]);
if (ndetected) {
- pr_err("blocking rcu_node structures:");
+ pr_err("blocking rcu_node structures (internal RCU debug):");
rcu_for_each_node_breadth_first(rnp) {
if (rnp == rnp_root)
continue; /* printed unconditionally */
{
struct task_struct *t = current;
+ lockdep_assert_irqs_disabled();
if (user || rcu_is_cpu_rrupt_from_idle()) {
rcu_note_voluntary_context_switch(current);
}
struct task_struct *t;
struct task_struct *ts[8];
+ lockdep_assert_irqs_disabled();
if (!rcu_preempt_blocked_readers_cgp(rnp))
return 0;
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
".q"[rscr.rs.b.need_qs],
".e"[rscr.rs.b.exp_hint],
".l"[rscr.on_blkd_list]);
+ lockdep_assert_irqs_disabled();
put_task_struct(t);
ndetected++;
}
rcu_for_each_leaf_node(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
for_each_leaf_node_possible_cpu(rnp, cpu)
- if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
- if (!trigger_single_cpu_backtrace(cpu))
+ if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
+ if (cpu_is_offline(cpu))
+ pr_err("Offline CPU %d blocking current GP.\n", cpu);
+ else if (!trigger_single_cpu_backtrace(cpu))
dump_cpu_task(cpu);
+ }
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
/* Complain about starvation of grace-period kthread. */
static void rcu_check_gp_kthread_starvation(void)
{
+ int cpu;
struct task_struct *gpk = rcu_state.gp_kthread;
unsigned long j;
if (rcu_is_gp_kthread_starving(&j)) {
+ cpu = gpk ? task_cpu(gpk) : -1;
pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
rcu_state.name, j,
(long)rcu_seq_current(&rcu_state.gp_seq),
data_race(rcu_state.gp_flags),
gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
- gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
+ gpk ? gpk->state : ~0, cpu);
if (gpk) {
pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name);
pr_err("RCU grace-period kthread stack dump:\n");
sched_show_task(gpk);
+ if (cpu >= 0) {
+ if (cpu_is_offline(cpu)) {
+ pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu);
+ } else {
+ pr_err("Stack dump where RCU GP kthread last ran:\n");
+ if (!trigger_single_cpu_backtrace(cpu))
+ dump_cpu_task(cpu);
+ }
+ }
wake_up_process(gpk);
}
}
}
+/* Complain about missing wakeups from expired fqs wait timer */
+static void rcu_check_gp_kthread_expired_fqs_timer(void)
+{
+ struct task_struct *gpk = rcu_state.gp_kthread;
+ short gp_state;
+ unsigned long jiffies_fqs;
+ int cpu;
+
+ /*
+ * Order reads of .gp_state and .jiffies_force_qs.
+ * Matching smp_wmb() is present in rcu_gp_fqs_loop().
+ */
+ gp_state = smp_load_acquire(&rcu_state.gp_state);
+ jiffies_fqs = READ_ONCE(rcu_state.jiffies_force_qs);
+
+ if (gp_state == RCU_GP_WAIT_FQS &&
+ time_after(jiffies, jiffies_fqs + RCU_STALL_MIGHT_MIN) &&
+ gpk && !READ_ONCE(gpk->on_rq)) {
+ cpu = task_cpu(gpk);
+ pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx\n",
+ rcu_state.name, (jiffies - jiffies_fqs),
+ (long)rcu_seq_current(&rcu_state.gp_seq),
+ data_race(rcu_state.gp_flags),
+ gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS,
+ gpk->state);
+ pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n",
+ cpu, kstat_softirqs_cpu(TIMER_SOFTIRQ, cpu));
+ }
+}
+
static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
{
int cpu;
struct rcu_node *rnp;
long totqlen = 0;
+ lockdep_assert_irqs_disabled();
+
/* Kick and suppress, if so configured. */
rcu_stall_kick_kthreads();
if (rcu_stall_is_suppressed())
}
}
ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock.
+ lockdep_assert_irqs_disabled();
}
for_each_possible_cpu(cpu)
WRITE_ONCE(rcu_state.jiffies_stall,
jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
+ rcu_check_gp_kthread_expired_fqs_timer();
rcu_check_gp_kthread_starvation();
panic_on_rcu_stall();
struct rcu_node *rnp = rcu_get_root();
long totqlen = 0;
+ lockdep_assert_irqs_disabled();
+
/* Kick and suppress, if so configured. */
rcu_stall_kick_kthreads();
if (rcu_stall_is_suppressed())
jiffies - gps,
(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
+ rcu_check_gp_kthread_expired_fqs_timer();
rcu_check_gp_kthread_starvation();
rcu_dump_cpu_stacks();
unsigned long js;
struct rcu_node *rnp;
+ lockdep_assert_irqs_disabled();
if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) ||
!rcu_gp_in_progress())
return;
#ifndef CONFIG_TINY_RCU
module_param(rcu_expedited, int, 0);
module_param(rcu_normal, int, 0);
-static int rcu_normal_after_boot;
+static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT);
+#ifndef CONFIG_PREEMPT_RT
module_param(rcu_normal_after_boot, int, 0);
+#endif
#endif /* #ifndef CONFIG_TINY_RCU */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static int scftorture_invoker(void *arg)
{
int cpu;
+ int curcpu;
DEFINE_TORTURE_RANDOM(rand);
struct scf_statistics *scfp = (struct scf_statistics *)arg;
bool was_offline = false;
VERBOSE_SCFTORTOUT("scftorture_invoker %d: Waiting for all SCF torturers from cpu %d", scfp->cpu, smp_processor_id());
// Make sure that the CPU is affinitized appropriately during testing.
- WARN_ON_ONCE(smp_processor_id() != scfp->cpu);
+ curcpu = smp_processor_id();
+ WARN_ONCE(curcpu != scfp->cpu % nr_cpu_ids,
+ "%s: Wanted CPU %d, running on %d, nr_cpu_ids = %d\n",
+ __func__, scfp->cpu, curcpu, nr_cpu_ids);
if (!atomic_dec_return(&n_started))
while (atomic_read_acquire(&n_started)) {
/**
* try_invoke_on_locked_down_task - Invoke a function on task in fixed state
- * @p: Process for which the function is to be invoked.
+ * @p: Process for which the function is to be invoked, can be @current.
* @func: Function to invoke.
* @arg: Argument to function.
*
*/
bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg)
{
- bool ret = false;
struct rq_flags rf;
+ bool ret = false;
struct rq *rq;
- lockdep_assert_irqs_enabled();
- raw_spin_lock_irq(&p->pi_lock);
+ raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
if (p->on_rq) {
rq = __task_rq_lock(p, &rf);
if (task_rq(p) == rq)
ret = func(p, arg);
}
}
- raw_spin_unlock_irq(&p->pi_lock);
+ raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
return ret;
}
static bool ftrace_dump_at_shutdown;
module_param(ftrace_dump_at_shutdown, bool, 0444);
+static int verbose_sleep_frequency;
+module_param(verbose_sleep_frequency, int, 0444);
+
+static int verbose_sleep_duration = 1;
+module_param(verbose_sleep_duration, int, 0444);
+
static char *torture_type;
static int verbose;
static int fullstop = FULLSTOP_RMMOD;
static DEFINE_MUTEX(fullstop_mutex);
+static atomic_t verbose_sleep_counter;
+
+/*
+ * Sleep if needed from VERBOSE_TOROUT*().
+ */
+void verbose_torout_sleep(void)
+{
+ if (verbose_sleep_frequency > 0 &&
+ verbose_sleep_duration > 0 &&
+ !(atomic_inc_return(&verbose_sleep_counter) % verbose_sleep_frequency))
+ schedule_timeout_uninterruptible(verbose_sleep_duration);
+}
+EXPORT_SYMBOL_GPL(verbose_torout_sleep);
+
+/*
+ * Schedule a high-resolution-timer sleep in nanoseconds, with a 32-bit
+ * nanosecond random fuzz. This function and its friends desynchronize
+ * testing from the timer wheel.
+ */
+int torture_hrtimeout_ns(ktime_t baset_ns, u32 fuzzt_ns, struct torture_random_state *trsp)
+{
+ ktime_t hto = baset_ns;
+
+ if (trsp)
+ hto += (torture_random(trsp) >> 3) % fuzzt_ns;
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ return schedule_hrtimeout(&hto, HRTIMER_MODE_REL);
+}
+EXPORT_SYMBOL_GPL(torture_hrtimeout_ns);
+
+/*
+ * Schedule a high-resolution-timer sleep in microseconds, with a 32-bit
+ * nanosecond (not microsecond!) random fuzz.
+ */
+int torture_hrtimeout_us(u32 baset_us, u32 fuzzt_ns, struct torture_random_state *trsp)
+{
+ ktime_t baset_ns = baset_us * NSEC_PER_USEC;
+
+ return torture_hrtimeout_ns(baset_ns, fuzzt_ns, trsp);
+}
+EXPORT_SYMBOL_GPL(torture_hrtimeout_us);
+
+/*
+ * Schedule a high-resolution-timer sleep in milliseconds, with a 32-bit
+ * microsecond (not millisecond!) random fuzz.
+ */
+int torture_hrtimeout_ms(u32 baset_ms, u32 fuzzt_us, struct torture_random_state *trsp)
+{
+ ktime_t baset_ns = baset_ms * NSEC_PER_MSEC;
+ u32 fuzzt_ns;
+
+ if ((u32)~0U / NSEC_PER_USEC < fuzzt_us)
+ fuzzt_ns = (u32)~0U;
+ else
+ fuzzt_ns = fuzzt_us * NSEC_PER_USEC;
+ return torture_hrtimeout_ns(baset_ns, fuzzt_ns, trsp);
+}
+EXPORT_SYMBOL_GPL(torture_hrtimeout_ms);
+
+/*
+ * Schedule a high-resolution-timer sleep in jiffies, with an
+ * implied one-jiffy random fuzz. This is intended to replace calls to
+ * schedule_timeout_interruptible() and friends.
+ */
+int torture_hrtimeout_jiffies(u32 baset_j, struct torture_random_state *trsp)
+{
+ ktime_t baset_ns = jiffies_to_nsecs(baset_j);
+
+ return torture_hrtimeout_ns(baset_ns, jiffies_to_nsecs(1), trsp);
+}
+EXPORT_SYMBOL_GPL(torture_hrtimeout_jiffies);
+
+/*
+ * Schedule a high-resolution-timer sleep in milliseconds, with a 32-bit
+ * millisecond (not second!) random fuzz.
+ */
+int torture_hrtimeout_s(u32 baset_s, u32 fuzzt_ms, struct torture_random_state *trsp)
+{
+ ktime_t baset_ns = baset_s * NSEC_PER_SEC;
+ u32 fuzzt_ns;
+
+ if ((u32)~0U / NSEC_PER_MSEC < fuzzt_ms)
+ fuzzt_ns = (u32)~0U;
+ else
+ fuzzt_ns = fuzzt_ms * NSEC_PER_MSEC;
+ return torture_hrtimeout_ns(baset_ns, fuzzt_ns, trsp);
+}
+EXPORT_SYMBOL_GPL(torture_hrtimeout_s);
+
#ifdef CONFIG_HOTPLUG_CPU
/*
static int min_online = -1;
static int max_online;
+static int torture_online_cpus = NR_CPUS;
+
+/*
+ * Some torture testing leverages confusion as to the number of online
+ * CPUs. This function returns the torture-testing view of this number,
+ * which allows torture tests to load-balance appropriately.
+ */
+int torture_num_online_cpus(void)
+{
+ return READ_ONCE(torture_online_cpus);
+}
+EXPORT_SYMBOL_GPL(torture_num_online_cpus);
+
/*
* Attempt to take a CPU offline. Return false if the CPU is already
* offline or if it is not subject to CPU-hotplug operations. The
*min_offl = delta;
if (*max_offl < delta)
*max_offl = delta;
+ WRITE_ONCE(torture_online_cpus, torture_online_cpus - 1);
+ WARN_ON_ONCE(torture_online_cpus <= 0);
}
return true;
*min_onl = delta;
if (*max_onl < delta)
*max_onl = delta;
+ WRITE_ONCE(torture_online_cpus, torture_online_cpus + 1);
}
return true;
}
EXPORT_SYMBOL_GPL(torture_online);
+/*
+ * Get everything online at the beginning and ends of tests.
+ */
+static void torture_online_all(char *phase)
+{
+ int cpu;
+ int ret;
+
+ for_each_possible_cpu(cpu) {
+ if (cpu_online(cpu))
+ continue;
+ ret = add_cpu(cpu);
+ if (ret && verbose) {
+ pr_alert("%s" TORTURE_FLAG
+ "%s: %s online %d: errno %d\n",
+ __func__, phase, torture_type, cpu, ret);
+ }
+ }
+}
+
/*
* Execute random CPU-hotplug operations at the interval specified
* by the onoff_interval.
int cpu;
int maxcpu = -1;
DEFINE_TORTURE_RANDOM(rand);
- int ret;
VERBOSE_TOROUT_STRING("torture_onoff task started");
for_each_online_cpu(cpu)
maxcpu = cpu;
WARN_ON(maxcpu < 0);
- if (!IS_MODULE(CONFIG_TORTURE_TEST)) {
- for_each_possible_cpu(cpu) {
- if (cpu_online(cpu))
- continue;
- ret = add_cpu(cpu);
- if (ret && verbose) {
- pr_alert("%s" TORTURE_FLAG
- "%s: Initial online %d: errno %d\n",
- __func__, torture_type, cpu, ret);
- }
- }
- }
-
+ torture_online_all("Initial");
if (maxcpu == 0) {
VERBOSE_TOROUT_STRING("Only one CPU, so CPU-hotplug testing is disabled");
goto stop;
stop:
torture_kthread_stopping("torture_onoff");
+ torture_online_all("Final");
return 0;
}
*/
bool stutter_wait(const char *title)
{
- ktime_t delay;
unsigned int i = 0;
bool ret = false;
int spt;
schedule_timeout_interruptible(1);
} else if (spt == 2) {
while (READ_ONCE(stutter_pause_test)) {
- if (!(i++ & 0xffff)) {
- set_current_state(TASK_INTERRUPTIBLE);
- delay = 10 * NSEC_PER_USEC;
- schedule_hrtimeout(&delay, HRTIMER_MODE_REL);
- }
+ if (!(i++ & 0xffff))
+ torture_hrtimeout_us(10, 0, NULL);
cond_resched();
}
} else {
*/
static int torture_stutter(void *arg)
{
- ktime_t delay;
DEFINE_TORTURE_RANDOM(rand);
int wtime;
if (stutter > 2) {
WRITE_ONCE(stutter_pause_test, 1);
wtime = stutter - 3;
- delay = ktime_divns(NSEC_PER_SEC * wtime, HZ);
- delay += (torture_random(&rand) >> 3) % NSEC_PER_MSEC;
- set_current_state(TASK_INTERRUPTIBLE);
- schedule_hrtimeout(&delay, HRTIMER_MODE_REL);
+ torture_hrtimeout_jiffies(wtime, &rand);
wtime = 2;
}
WRITE_ONCE(stutter_pause_test, 2);
- delay = ktime_divns(NSEC_PER_SEC * wtime, HZ);
- set_current_state(TASK_INTERRUPTIBLE);
- schedule_hrtimeout(&delay, HRTIMER_MODE_REL);
+ torture_hrtimeout_jiffies(wtime, NULL);
}
WRITE_ONCE(stutter_pause_test, 0);
if (!torture_must_stop())
- schedule_timeout_interruptible(stutter_gap);
+ torture_hrtimeout_jiffies(stutter_gap, NULL);
torture_shutdown_absorb("torture_stutter");
} while (!torture_must_stop());
torture_kthread_stopping("torture_stutter");
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/slab.h>
+#include <linux/mm.h>
#include <linux/percpu-refcount.h>
/*
struct percpu_ref_data, rcu);
struct percpu_ref *ref = data->ref;
unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
+ static atomic_t underflows;
unsigned long count = 0;
int cpu;
*/
atomic_long_add((long)count - PERCPU_COUNT_BIAS, &data->count);
- WARN_ONCE(atomic_long_read(&data->count) <= 0,
- "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
- data->release, atomic_long_read(&data->count));
+ if (WARN_ONCE(atomic_long_read(&data->count) <= 0,
+ "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
+ data->release, atomic_long_read(&data->count)) &&
+ atomic_inc_return(&underflows) < 4) {
+ pr_err("%s(): percpu_ref underflow", __func__);
+ mem_dump_obj(data);
+ }
/* @ref is viewed as dead on all CPUs, send out switch confirmation */
percpu_ref_call_confirm_rcu(rcu);
EXPORT_SYMBOL(__kmalloc_node_track_caller);
#endif /* CONFIG_NUMA */
+void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+{
+ struct kmem_cache *cachep;
+ unsigned int objnr;
+ void *objp;
+
+ kpp->kp_ptr = object;
+ kpp->kp_page = page;
+ cachep = page->slab_cache;
+ kpp->kp_slab_cache = cachep;
+ objp = object - obj_offset(cachep);
+ kpp->kp_data_offset = obj_offset(cachep);
+ page = virt_to_head_page(objp);
+ objnr = obj_to_index(cachep, page, objp);
+ objp = index_to_obj(cachep, page, objnr);
+ kpp->kp_objp = objp;
+ if (DEBUG && cachep->flags & SLAB_STORE_USER)
+ kpp->kp_ret = *dbg_userword(cachep, objp);
+}
+
/**
* __do_kmalloc - allocate memory
* @size: how many bytes of memory are required.
return false;
}
+#define KS_ADDRS_COUNT 16
+struct kmem_obj_info {
+ void *kp_ptr;
+ struct page *kp_page;
+ void *kp_objp;
+ unsigned long kp_data_offset;
+ struct kmem_cache *kp_slab_cache;
+ void *kp_ret;
+ void *kp_stack[KS_ADDRS_COUNT];
+};
+void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page);
+
#endif /* MM_SLAB_H */
return slab_state >= UP;
}
+/**
+ * kmem_valid_obj - does the pointer reference a valid slab object?
+ * @object: pointer to query.
+ *
+ * Return: %true if the pointer is to a not-yet-freed object from
+ * kmalloc() or kmem_cache_alloc(), either %true or %false if the pointer
+ * is to an already-freed object, and %false otherwise.
+ */
+bool kmem_valid_obj(void *object)
+{
+ struct page *page;
+
+ /* Some arches consider ZERO_SIZE_PTR to be a valid address. */
+ if (object < (void *)PAGE_SIZE || !virt_addr_valid(object))
+ return false;
+ page = virt_to_head_page(object);
+ return PageSlab(page);
+}
+
+/**
+ * kmem_dump_obj - Print available slab provenance information
+ * @object: slab object for which to find provenance information.
+ *
+ * This function uses pr_cont(), so that the caller is expected to have
+ * printed out whatever preamble is appropriate. The provenance information
+ * depends on the type of object and on how much debugging is enabled.
+ * For a slab-cache object, the fact that it is a slab object is printed,
+ * and, if available, the slab name, return address, and stack trace from
+ * the allocation of that object.
+ *
+ * This function will splat if passed a pointer to a non-slab object.
+ * If you are not sure what type of object you have, you should instead
+ * use mem_dump_obj().
+ */
+void kmem_dump_obj(void *object)
+{
+ char *cp = IS_ENABLED(CONFIG_MMU) ? "" : "/vmalloc";
+ int i;
+ struct page *page;
+ unsigned long ptroffset;
+ struct kmem_obj_info kp = { };
+
+ if (WARN_ON_ONCE(!virt_addr_valid(object)))
+ return;
+ page = virt_to_head_page(object);
+ if (WARN_ON_ONCE(!PageSlab(page))) {
+ pr_cont(" non-slab memory.\n");
+ return;
+ }
+ kmem_obj_info(&kp, object, page);
+ if (kp.kp_slab_cache)
+ pr_cont(" slab%s %s", cp, kp.kp_slab_cache->name);
+ else
+ pr_cont(" slab%s", cp);
+ if (kp.kp_objp)
+ pr_cont(" start %px", kp.kp_objp);
+ if (kp.kp_data_offset)
+ pr_cont(" data offset %lu", kp.kp_data_offset);
+ if (kp.kp_objp) {
+ ptroffset = ((char *)object - (char *)kp.kp_objp) - kp.kp_data_offset;
+ pr_cont(" pointer offset %lu", ptroffset);
+ }
+ if (kp.kp_slab_cache && kp.kp_slab_cache->usersize)
+ pr_cont(" size %u", kp.kp_slab_cache->usersize);
+ if (kp.kp_ret)
+ pr_cont(" allocated at %pS\n", kp.kp_ret);
+ else
+ pr_cont("\n");
+ for (i = 0; i < ARRAY_SIZE(kp.kp_stack); i++) {
+ if (!kp.kp_stack[i])
+ break;
+ pr_info(" %pS\n", kp.kp_stack[i]);
+ }
+}
+
#ifndef CONFIG_SLOB
/* Create a cache during boot when no slab services are available yet */
void __init create_boot_cache(struct kmem_cache *s, const char *name,
spin_unlock_irqrestore(&slob_lock, flags);
}
+void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+{
+ kpp->kp_ptr = object;
+ kpp->kp_page = page;
+}
+
/*
* End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
*/
return 0;
}
+void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+{
+ void *base;
+ int __maybe_unused i;
+ unsigned int objnr;
+ void *objp;
+ void *objp0;
+ struct kmem_cache *s = page->slab_cache;
+ struct track __maybe_unused *trackp;
+
+ kpp->kp_ptr = object;
+ kpp->kp_page = page;
+ kpp->kp_slab_cache = s;
+ base = page_address(page);
+ objp0 = kasan_reset_tag(object);
+#ifdef CONFIG_SLUB_DEBUG
+ objp = restore_red_left(s, objp0);
+#else
+ objp = objp0;
+#endif
+ objnr = obj_to_index(s, page, objp);
+ kpp->kp_data_offset = (unsigned long)((char *)objp0 - (char *)objp);
+ objp = base + s->size * objnr;
+ kpp->kp_objp = objp;
+ if (WARN_ON_ONCE(objp < base || objp >= base + page->objects * s->size || (objp - base) % s->size) ||
+ !(s->flags & SLAB_STORE_USER))
+ return;
+#ifdef CONFIG_SLUB_DEBUG
+ trackp = get_track(s, objp, TRACK_ALLOC);
+ kpp->kp_ret = (void *)trackp->addr;
+#ifdef CONFIG_STACKTRACE
+ for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
+ kpp->kp_stack[i] = (void *)trackp->addrs[i];
+ if (!kpp->kp_stack[i])
+ break;
+ }
+#endif
+#endif
+}
+
/********************************************************************
* Kmalloc subsystem
*******************************************************************/
kunmap_atomic(addr1);
return ret;
}
+
+/**
+ * mem_dump_obj - Print available provenance information
+ * @object: object for which to find provenance information.
+ *
+ * This function uses pr_cont(), so that the caller is expected to have
+ * printed out whatever preamble is appropriate. The provenance information
+ * depends on the type of object and on how much debugging is enabled.
+ * For example, for a slab-cache object, the slab name is printed, and,
+ * if available, the return address and stack trace from the allocation
+ * of that object.
+ */
+void mem_dump_obj(void *object)
+{
+ if (kmem_valid_obj(object)) {
+ kmem_dump_obj(object);
+ return;
+ }
+ if (vmalloc_dump_obj(object))
+ return;
+ if (!virt_addr_valid(object)) {
+ if (object == NULL)
+ pr_cont(" NULL pointer.\n");
+ else if (object == ZERO_SIZE_PTR)
+ pr_cont(" zero-size pointer.\n");
+ else
+ pr_cont(" non-paged memory.\n");
+ return;
+ }
+ pr_cont(" non-slab/vmalloc memory.\n");
+}
}
#endif /* CONFIG_SMP */
+bool vmalloc_dump_obj(void *object)
+{
+ struct vm_struct *vm;
+ void *objp = (void *)PAGE_ALIGN((unsigned long)object);
+
+ vm = find_vm_area(objp);
+ if (!vm)
+ return false;
+ pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n",
+ vm->nr_pages, (unsigned long)vm->addr, vm->caller);
+ return true;
+}
+
#ifdef CONFIG_PROC_FS
static void *s_start(struct seq_file *m, loff_t *pos)
__acquires(&vmap_purge_lock)
--- /dev/null
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Create a spreadsheet from torture-test Kconfig options and kernel boot
+# parameters. Run this in the directory containing the scenario files.
+#
+# Usage: config2csv path.csv [ "scenario1 scenario2 ..." ]
+#
+# By default, this script will take the list of scenarios from the CFLIST
+# file in that directory, otherwise it will consider only the scenarios
+# specified on the command line. It will examine each scenario's file
+# and also its .boot file, if present, and create a column in the .csv
+# output file. Note that "CFLIST" is a synonym for all the scenarios in the
+# CFLIST file, which allows easy comparison of those scenarios with selected
+# scenarios such as BUSTED that are normally omitted from CFLIST files.
+
+csvout=${1}
+if test -z "$csvout"
+then
+ echo "Need .csv output file as first argument."
+ exit 1
+fi
+shift
+defaultconfigs="`tr '\012' ' ' < CFLIST`"
+if test "$#" -eq 0
+then
+ scenariosarg=$defaultconfigs
+else
+ scenariosarg=$*
+fi
+scenarios="`echo $scenariosarg | sed -e "s/\<CFLIST\>/$defaultconfigs/g"`"
+
+T=/tmp/config2latex.sh.$$
+trap 'rm -rf $T' 0
+mkdir $T
+
+cat << '---EOF---' >> $T/p.awk
+END {
+---EOF---
+for i in $scenarios
+do
+ echo ' s["'$i'"] = 1;' >> $T/p.awk
+ grep -v '^#' < $i | grep -v '^ *$' > $T/p
+ if test -r $i.boot
+ then
+ tr -s ' ' '\012' < $i.boot | grep -v '^#' >> $T/p
+ fi
+ sed -e 's/^[^=]*$/&=?/' < $T/p |
+ sed -e 's/^\([^=]*\)=\(.*\)$/\tp["\1:'"$i"'"] = "\2";\n\tc["\1"] = 1;/' >> $T/p.awk
+done
+cat << '---EOF---' >> $T/p.awk
+ ns = asorti(s, ss);
+ nc = asorti(c, cs);
+ for (j = 1; j <= ns; j++)
+ printf ",\"%s\"", ss[j];
+ printf "\n";
+ for (i = 1; i <= nc; i++) {
+ printf "\"%s\"", cs[i];
+ for (j = 1; j <= ns; j++) {
+ printf ",\"%s\"", p[cs[i] ":" ss[j]];
+ }
+ printf "\n";
+ }
+}
+---EOF---
+awk -f $T/p.awk < /dev/null > $T/p.csv
+cp $T/p.csv $csvout
grep -v 'ODEBUG: ' |
grep -v 'This means that this is a DEBUG kernel and it is' |
grep -v 'Warning: unable to open an initial console' |
+grep -v 'Warning: Failed to add ttynull console. No stdin, stdout, and stderr.*the init process!' |
grep -v 'NOHZ tick-stop error: Non-RCU local softirq work is pending, handler'
grep -q '^CONFIG_HOTPLUG_CPU=y$' "$1"
}
+# get_starttime
+#
+# Returns a cookie identifying the current time.
+get_starttime () {
+ awk 'BEGIN { print systime() }' < /dev/null
+}
+
+# get_starttime_duration starttime
+#
+# Given the return value from get_starttime, compute a human-readable
+# string denoting the time since get_starttime.
+get_starttime_duration () {
+ awk -v starttime=$1 '
+ BEGIN {
+ ts = systime() - starttime;
+ tm = int(ts / 60);
+ th = int(ts / 3600);
+ td = int(ts / 86400);
+ d = td;
+ h = th - td * 24;
+ m = tm - th * 60;
+ s = ts - tm * 60;
+ if (d >= 1)
+ printf "%dd %d:%02d:%02d\n", d, h, m, s
+ else if (h >= 1)
+ printf "%d:%02d:%02d\n", h, m, s
+ else if (m >= 1)
+ printf "%d:%02d.0\n", m, s
+ else
+ print s " seconds"
+ }' < /dev/null
+}
+
# identify_boot_image qemu-cmd
#
# Returns the relative path to the kernel build image. This will be
# and the TORTURE_QEMU_INTERACTIVE environment variable.
identify_qemu_append () {
echo debug_boot_weak_hash
+ echo panic=-1
local console=ttyS0
case "$1" in
qemu-system-x86_64|qemu-system-i386)
# Returns the number of virtual CPUs available to the aggregate of the
# guest OSes.
identify_qemu_vcpus () {
- lscpu | grep '^CPU(s):' | sed -e 's/CPU(s)://' -e 's/[ ]*//g'
+ getconf _NPROCESSORS_ONLN
}
# print_bug
if test -n "$files"
then
$editor $files
+ editorret=1
else
echo No build errors.
fi
if grep -q -e "--buildonly" < ${rundir}/log
then
echo Build-only run, no console logs to check.
+ exit $editorret
fi
# Find console logs with errors
exit 1
else
echo No errors in console logs.
- exit 0
+ if test -n "$editorret"
+ then
+ exit $editorret
+ else
+ exit 0
+ fi
fi
fi
done
EDITOR=echo kvm-find-errors.sh "${@: -1}" > $T 2>&1
-ret=$?
builderrors="`tr ' ' '\012' < $T | grep -c '/Make.out.diags'`"
if test "$builderrors" -gt 0
then
echo $builderrors runs with build errors.
+ ret=1
fi
runerrors="`tr ' ' '\012' < $T | grep -c '/console.log.diags'`"
if test "$runerrors" -gt 0
then
echo $runerrors runs with runtime errors.
+ ret=2
fi
exit $ret
qemu_args=$5
boot_args=$6
-kstarttime=`gawk 'BEGIN { print systime() }' < /dev/null`
if test -z "$TORTURE_BUILDONLY"
then
echo ' ---' `date`: Starting kernel
boot_args="$boot_args $TORTURE_BOOT_GDB_ARG"
fi
echo $QEMU $qemu_args -m $TORTURE_QEMU_MEM -kernel $KERNEL -append \"$qemu_append $boot_args\" $TORTURE_QEMU_GDB_ARG > $resdir/qemu-cmd
+echo "# TORTURE_SHUTDOWN_GRACE=$TORTURE_SHUTDOWN_GRACE" >> $resdir/qemu-cmd
+echo "# seconds=$seconds" >> $resdir/qemu-cmd
if test -n "$TORTURE_BUILDONLY"
then
echo "NOTE: $QEMU either did not run or was interactive" > $resdir/console.log
# Attempt to run qemu
+kstarttime=`gawk 'BEGIN { print systime() }' < /dev/null`
( . $T/qemu-cmd; wait `cat $resdir/qemu_pid`; echo $? > $resdir/qemu-retval ) &
commandcompleted=0
if test -z "$TORTURE_KCONFIG_GDB_ARG"
if test -n "$TORTURE_KCONFIG_GDB_ARG"
then
:
- elif test $kruntime -ge $seconds || test -f "$TORTURE_STOPFILE"
+ elif test $kruntime -ge $seconds || test -f "$resdir/../STOP.1"
then
break;
fi
fi
if test $commandcompleted -eq 0 -a -n "$qemu_pid"
then
- if ! test -f "$TORTURE_STOPFILE"
+ if ! test -f "$resdir/../STOP.1"
then
echo Grace period for qemu job at pid $qemu_pid
fi
oldline="`tail $resdir/console.log`"
while :
do
- if test -f "$TORTURE_STOPFILE"
+ if test -f "$resdir/../STOP.1"
then
- echo "PID $qemu_pid killed due to run STOP request" >> $resdir/Warnings 2>&1
+ echo "PID $qemu_pid killed due to run STOP.1 request" >> $resdir/Warnings 2>&1
kill -KILL $qemu_pid
break
fi
ds=`date +%Y.%m.%d-%H.%M.%S`
jitter="-1"
+startdate="`date`"
+starttime="`get_starttime`"
+
usage () {
echo "Usage: $scriptname optional arguments:"
echo " --allcpus"
echo " --cpus N"
echo " --datestamp string"
echo " --defconfig string"
- echo " --dryrun sched|script"
+ echo " --dryrun batches|sched|script"
echo " --duration minutes | <seconds>s | <hours>h | <days>d"
echo " --gdb"
echo " --help"
;;
--bootargs|--bootarg)
checkarg --bootargs "(list of kernel boot arguments)" "$#" "$2" '.*' '^--'
- TORTURE_BOOTARGS="$2"
+ TORTURE_BOOTARGS="$TORTURE_BOOTARGS $2"
shift
;;
--bootimage)
TORTURE_BUILDONLY=1
;;
--configs|--config)
- checkarg --configs "(list of config files)" "$#" "$2" '^[^/]*$' '^--'
- configs="$2"
+ checkarg --configs "(list of config files)" "$#" "$2" '^[^/]\+$' '^--'
+ configs="$configs $2"
shift
;;
--cpus)
shift
;;
--datestamp)
- checkarg --datestamp "(relative pathname)" "$#" "$2" '^[^/]*$' '^--'
+ checkarg --datestamp "(relative pathname)" "$#" "$2" '^[a-zA-Z0-9._-/]*$' '^--'
ds=$2
shift
;;
shift
;;
--dryrun)
- checkarg --dryrun "sched|script" $# "$2" 'sched\|script' '^--'
+ checkarg --dryrun "batches|sched|script" $# "$2" 'batches\|sched\|script' '^--'
dryrun=$2
shift
;;
;;
--kconfig|--kconfigs)
checkarg --kconfig "(Kconfig options)" $# "$2" '^CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\( CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\)*$' '^error$'
- TORTURE_KCONFIG_ARG="$2"
+ TORTURE_KCONFIG_ARG="`echo "$TORTURE_KCONFIG_ARG $2" | sed -e 's/^ *//' -e 's/ *$//'`"
shift
;;
--kasan)
TORTURE_KCONFIG_KASAN_ARG="CONFIG_DEBUG_INFO=y CONFIG_KASAN=y"; export TORTURE_KCONFIG_KASAN_ARG
;;
--kcsan)
- TORTURE_KCONFIG_KCSAN_ARG="CONFIG_DEBUG_INFO=y CONFIG_KCSAN=y CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY=n CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000 CONFIG_KCSAN_VERBOSE=y CONFIG_KCSAN_INTERRUPT_WATCHER=y"; export TORTURE_KCONFIG_KCSAN_ARG
+ TORTURE_KCONFIG_KCSAN_ARG="CONFIG_DEBUG_INFO=y CONFIG_KCSAN=y CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY=n CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000 CONFIG_KCSAN_INTERRUPT_WATCHER=y CONFIG_KCSAN_VERBOSE=y CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y"; export TORTURE_KCONFIG_KCSAN_ARG
;;
--kmake-arg|--kmake-args)
checkarg --kmake-arg "(kernel make arguments)" $# "$2" '.*' '^error$'
- TORTURE_KMAKE_ARG="$2"
+ TORTURE_KMAKE_ARG="`echo "$TORTURE_KMAKE_ARG $2" | sed -e 's/^ *//' -e 's/ *$//'`"
shift
;;
--mac)
;;
--qemu-args|--qemu-arg)
checkarg --qemu-args "(qemu arguments)" $# "$2" '^-' '^error'
- TORTURE_QEMU_ARG="$2"
+ TORTURE_QEMU_ARG="`echo "$TORTURE_QEMU_ARG $2" | sed -e 's/^ *//' -e 's/ *$//'`"
shift
;;
--qemu-cmd)
shift
done
-if test -z "$TORTURE_INITRD" || tools/testing/selftests/rcutorture/bin/mkinitrd.sh
+if test -n "$dryrun" || test -z "$TORTURE_INITRD" || tools/testing/selftests/rcutorture/bin/mkinitrd.sh
then
:
else
exit 1
fi
fi
-for CF1 in $configs_derep
+echo 'BEGIN {' > $T/cfgcpu.awk
+for CF1 in `echo $configs_derep | tr -s ' ' '\012' | sort -u`
do
if test -f "$CONFIGFRAG/$CF1"
then
- cpu_count=`configNR_CPUS.sh $CONFIGFRAG/$CF1`
+ if echo "$TORTURE_KCONFIG_ARG" | grep -q '\<CONFIG_NR_CPUS='
+ then
+ echo "$TORTURE_KCONFIG_ARG" | tr -s ' ' | tr ' ' '\012' > $T/KCONFIG_ARG
+ cpu_count=`configNR_CPUS.sh $T/KCONFIG_ARG`
+ else
+ cpu_count=`configNR_CPUS.sh $CONFIGFRAG/$CF1`
+ fi
cpu_count=`configfrag_boot_cpus "$TORTURE_BOOTARGS" "$CONFIGFRAG/$CF1" "$cpu_count"`
cpu_count=`configfrag_boot_maxcpus "$TORTURE_BOOTARGS" "$CONFIGFRAG/$CF1" "$cpu_count"`
- echo $CF1 $cpu_count >> $T/cfgcpu
+ echo 'scenariocpu["'"$CF1"'"] = '"$cpu_count"';' >> $T/cfgcpu.awk
else
echo "The --configs file $CF1 does not exist, terminating."
exit 1
fi
done
+cat << '___EOF___' >> $T/cfgcpu.awk
+}
+{
+ for (i = 1; i <= NF; i++)
+ print $i, scenariocpu[$i];
+}
+___EOF___
+echo $configs_derep | awk -f $T/cfgcpu.awk > $T/cfgcpu
sort -k2nr $T/cfgcpu -T="$T" > $T/cfgcpu.sort
# Use a greedy bin-packing algorithm, sorting the list accordingly.
batch = 0;
nc = -1;
- # Each pass through the following loop creates on test batch
- # that can be executed concurrently given ncpus. Note that a
- # given test that requires more than the available CPUs will run in
- # their own batch. Such tests just have to make do with what
- # is available.
+ # Each pass through the following loop creates on test batch that
+ # can be executed concurrently given ncpus. Note that a given test
+ # that requires more than the available CPUs will run in its own
+ # batch. Such tests just have to make do with what is available.
while (nc != ncpus) {
batch++;
nc = ncpus;
then
mkdir -p "$resdir" || :
fi
-mkdir $resdir/$ds
+mkdir -p $resdir/$ds
TORTURE_RESDIR="$resdir/$ds"; export TORTURE_RESDIR
-TORTURE_STOPFILE="$resdir/$ds/STOP"; export TORTURE_STOPFILE
+TORTURE_STOPFILE="$resdir/$ds/STOP.1"; export TORTURE_STOPFILE
echo Results directory: $resdir/$ds
echo $scriptname $args
touch $resdir/$ds/log
dump(first, i, batchnum);
}' >> $T/script
+cat << '___EOF___' >> $T/script
+echo | tee -a $TORTURE_RESDIR/log
+echo | tee -a $TORTURE_RESDIR/log
+echo " --- `date` Test summary:" | tee -a $TORTURE_RESDIR/log
+___EOF___
cat << ___EOF___ >> $T/script
-echo
-echo
-echo " --- `date` Test summary:"
-echo Results directory: $resdir/$ds
-kcsan-collapse.sh $resdir/$ds
-kvm-recheck.sh $resdir/$ds
+echo Results directory: $resdir/$ds | tee -a $resdir/$ds/log
+kcsan-collapse.sh $resdir/$ds | tee -a $resdir/$ds/log
+kvm-recheck.sh $resdir/$ds > $T/kvm-recheck.sh.out 2>&1
___EOF___
+echo 'ret=$?' >> $T/script
+echo "cat $T/kvm-recheck.sh.out | tee -a $resdir/$ds/log" >> $T/script
+echo 'exit $ret' >> $T/script
if test "$dryrun" = script
then
elif test "$dryrun" = sched
then
# Extract the test run schedule from the script.
- egrep 'Start batch|Starting build\.' $T/script |
- grep -v ">>" |
+ egrep 'Start batch|Starting build\.' $T/script | grep -v ">>" |
sed -e 's/:.*$//' -e 's/^echo //'
+ nbuilds="`grep 'Starting build\.' $T/script |
+ grep -v ">>" | sed -e 's/:.*$//' -e 's/^echo //' |
+ awk '{ print $1 }' | grep -v '\.' | wc -l`"
+ echo Total number of builds: $nbuilds
+ nbatches="`grep 'Start batch' $T/script | grep -v ">>" | wc -l`"
+ echo Total number of batches: $nbatches
exit 0
+elif test "$dryrun" = batches
+then
+ # Extract the tests and their batches from the script.
+ egrep 'Start batch|Starting build\.' $T/script | grep -v ">>" |
+ sed -e 's/:.*$//' -e 's/^echo //' -e 's/-ovf//' |
+ awk '
+ /^----Start/ {
+ batchno = $3;
+ next;
+ }
+ {
+ print batchno, $1, $2
+ }'
else
# Not a dryrun, so run the script.
- sh $T/script
+ bash $T/script
+ ret=$?
+ echo " --- Done at `date` (`get_starttime_duration $starttime`) exitcode $ret" | tee -a $resdir/$ds/log
+ exit $ret
fi
# Tracing: trace_event=rcu:rcu_grace_period,rcu:rcu_future_grace_period,rcu:rcu_grace_period_init,rcu:rcu_nocb_wake,rcu:rcu_preempt_task,rcu:rcu_unlock_preempted_task,rcu:rcu_quiescent_state_report,rcu:rcu_fqs,rcu:rcu_callback,rcu:rcu_kfree_callback,rcu:rcu_batch_start,rcu:rcu_invoke_callback,rcu:rcu_invoke_kfree_callback,rcu:rcu_batch_end,rcu:rcu_torture_read,rcu:rcu_barrier
. functions.sh
-if grep -q CC < $F || test -n "$TORTURE_TRUST_MAKE"
+if grep -q CC < $F || test -n "$TORTURE_TRUST_MAKE" || grep -qe --trust-make < `dirname $F`/../log
then
:
else
then
summary="$summary Badness: $n_badness"
fi
- n_warn=`grep -v 'Warning: unable to open an initial console' $file | egrep -c 'WARNING:|Warn'`
+ n_warn=`grep -v 'Warning: unable to open an initial console' $file | grep -v 'Warning: Failed to add ttynull console. No stdin, stdout, and stderr for the init process' | egrep -c 'WARNING:|Warn'`
if test "$n_warn" -ne 0
then
summary="$summary Warnings: $n_warn"
--- /dev/null
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Run a series of torture tests, intended for overnight or
+# longer timeframes, and also for large systems.
+#
+# Usage: torture.sh [ options ]
+#
+# Copyright (C) 2020 Facebook, Inc.
+#
+# Authors: Paul E. McKenney <paulmck@kernel.org>
+
+scriptname=$0
+args="$*"
+
+KVM="`pwd`/tools/testing/selftests/rcutorture"; export KVM
+PATH=${KVM}/bin:$PATH; export PATH
+. functions.sh
+
+TORTURE_ALLOTED_CPUS="`identify_qemu_vcpus`"
+MAKE_ALLOTED_CPUS=$((TORTURE_ALLOTED_CPUS*2))
+HALF_ALLOTED_CPUS=$((TORTURE_ALLOTED_CPUS/2))
+if test "$HALF_ALLOTED_CPUS" -lt 1
+then
+ HALF_ALLOTED_CPUS=1
+fi
+VERBOSE_BATCH_CPUS=$((TORTURE_ALLOTED_CPUS/16))
+if test "$VERBOSE_BATCH_CPUS" -lt 2
+then
+ VERBOSE_BATCH_CPUS=0
+fi
+
+# Configurations/scenarios.
+configs_rcutorture=
+configs_locktorture=
+configs_scftorture=
+kcsan_kmake_args=
+
+# Default compression, duration, and apportionment.
+compress_kasan_vmlinux="`identify_qemu_vcpus`"
+duration_base=10
+duration_rcutorture_frac=7
+duration_locktorture_frac=1
+duration_scftorture_frac=2
+
+# "yes" or "no" parameters
+do_allmodconfig=yes
+do_rcutorture=yes
+do_locktorture=yes
+do_scftorture=yes
+do_rcuscale=yes
+do_refscale=yes
+do_kvfree=yes
+do_kasan=yes
+do_kcsan=no
+
+# doyesno - Helper function for yes/no arguments
+function doyesno () {
+ if test "$1" = "$2"
+ then
+ echo yes
+ else
+ echo no
+ fi
+}
+
+usage () {
+ echo "Usage: $scriptname optional arguments:"
+ echo " --compress-kasan-vmlinux concurrency"
+ echo " --configs-rcutorture \"config-file list w/ repeat factor (3*TINY01)\""
+ echo " --configs-locktorture \"config-file list w/ repeat factor (10*LOCK01)\""
+ echo " --configs-scftorture \"config-file list w/ repeat factor (2*CFLIST)\""
+ echo " --doall"
+ echo " --doallmodconfig / --do-no-allmodconfig"
+ echo " --do-kasan / --do-no-kasan"
+ echo " --do-kcsan / --do-no-kcsan"
+ echo " --do-kvfree / --do-no-kvfree"
+ echo " --do-locktorture / --do-no-locktorture"
+ echo " --do-none"
+ echo " --do-rcuscale / --do-no-rcuscale"
+ echo " --do-rcutorture / --do-no-rcutorture"
+ echo " --do-refscale / --do-no-refscale"
+ echo " --do-scftorture / --do-no-scftorture"
+ echo " --duration [ <minutes> | <hours>h | <days>d ]"
+ echo " --kcsan-kmake-arg kernel-make-arguments"
+ exit 1
+}
+
+while test $# -gt 0
+do
+ case "$1" in
+ --compress-kasan-vmlinux)
+ checkarg --compress-kasan-vmlinux "(concurrency level)" $# "$2" '^[0-9][0-9]*$' '^error'
+ compress_kasan_vmlinux=$2
+ shift
+ ;;
+ --config-rcutorture|--configs-rcutorture)
+ checkarg --configs-rcutorture "(list of config files)" "$#" "$2" '^[^/]\+$' '^--'
+ configs_rcutorture="$configs_rcutorture $2"
+ shift
+ ;;
+ --config-locktorture|--configs-locktorture)
+ checkarg --configs-locktorture "(list of config files)" "$#" "$2" '^[^/]\+$' '^--'
+ configs_locktorture="$configs_locktorture $2"
+ shift
+ ;;
+ --config-scftorture|--configs-scftorture)
+ checkarg --configs-scftorture "(list of config files)" "$#" "$2" '^[^/]\+$' '^--'
+ configs_scftorture="$configs_scftorture $2"
+ shift
+ ;;
+ --doall)
+ do_allmodconfig=yes
+ do_rcutorture=yes
+ do_locktorture=yes
+ do_scftorture=yes
+ do_rcuscale=yes
+ do_refscale=yes
+ do_kvfree=yes
+ do_kasan=yes
+ do_kcsan=yes
+ ;;
+ --do-allmodconfig|--do-no-allmodconfig)
+ do_allmodconfig=`doyesno "$1" --do-allmodconfig`
+ ;;
+ --do-kasan|--do-no-kasan)
+ do_kasan=`doyesno "$1" --do-kasan`
+ ;;
+ --do-kcsan|--do-no-kcsan)
+ do_kcsan=`doyesno "$1" --do-kcsan`
+ ;;
+ --do-kvfree|--do-no-kvfree)
+ do_kvfree=`doyesno "$1" --do-kvfree`
+ ;;
+ --do-locktorture|--do-no-locktorture)
+ do_locktorture=`doyesno "$1" --do-locktorture`
+ ;;
+ --do-none)
+ do_allmodconfig=no
+ do_rcutorture=no
+ do_locktorture=no
+ do_scftorture=no
+ do_rcuscale=no
+ do_refscale=no
+ do_kvfree=no
+ do_kasan=no
+ do_kcsan=no
+ ;;
+ --do-rcuscale|--do-no-rcuscale)
+ do_rcuscale=`doyesno "$1" --do-rcuscale`
+ ;;
+ --do-rcutorture|--do-no-rcutorture)
+ do_rcutorture=`doyesno "$1" --do-rcutorture`
+ ;;
+ --do-refscale|--do-no-refscale)
+ do_refscale=`doyesno "$1" --do-refscale`
+ ;;
+ --do-scftorture|--do-no-scftorture)
+ do_scftorture=`doyesno "$1" --do-scftorture`
+ ;;
+ --duration)
+ checkarg --duration "(minutes)" $# "$2" '^[0-9][0-9]*\(m\|h\|d\|\)$' '^error'
+ mult=1
+ if echo "$2" | grep -q 'm$'
+ then
+ mult=1
+ elif echo "$2" | grep -q 'h$'
+ then
+ mult=60
+ elif echo "$2" | grep -q 'd$'
+ then
+ mult=1440
+ fi
+ ts=`echo $2 | sed -e 's/[smhd]$//'`
+ duration_base=$(($ts*mult))
+ shift
+ ;;
+ --kcsan-kmake-arg|--kcsan-kmake-args)
+ checkarg --kcsan-kmake-arg "(kernel make arguments)" $# "$2" '.*' '^error$'
+ kcsan_kmake_args="`echo "$kcsan_kmake_args $2" | sed -e 's/^ *//' -e 's/ *$//'`"
+ shift
+ ;;
+ *)
+ echo Unknown argument $1
+ usage
+ ;;
+ esac
+ shift
+done
+
+ds="`date +%Y.%m.%d-%H.%M.%S`-torture"
+startdate="`date`"
+starttime="`get_starttime`"
+
+T=/tmp/torture.sh.$$
+trap 'rm -rf $T' 0 2
+mkdir $T
+
+echo " --- " $scriptname $args | tee -a $T/log
+echo " --- Results directory: " $ds | tee -a $T/log
+
+# Calculate rcutorture defaults and apportion time
+if test -z "$configs_rcutorture"
+then
+ configs_rcutorture=CFLIST
+fi
+duration_rcutorture=$((duration_base*duration_rcutorture_frac/10))
+if test "$duration_rcutorture" -eq 0
+then
+ echo " --- Zero time for rcutorture, disabling" | tee -a $T/log
+ do_rcutorture=no
+fi
+
+# Calculate locktorture defaults and apportion time
+if test -z "$configs_locktorture"
+then
+ configs_locktorture=CFLIST
+fi
+duration_locktorture=$((duration_base*duration_locktorture_frac/10))
+if test "$duration_locktorture" -eq 0
+then
+ echo " --- Zero time for locktorture, disabling" | tee -a $T/log
+ do_locktorture=no
+fi
+
+# Calculate scftorture defaults and apportion time
+if test -z "$configs_scftorture"
+then
+ configs_scftorture=CFLIST
+fi
+duration_scftorture=$((duration_base*duration_scftorture_frac/10))
+if test "$duration_scftorture" -eq 0
+then
+ echo " --- Zero time for scftorture, disabling" | tee -a $T/log
+ do_scftorture=no
+fi
+
+touch $T/failures
+touch $T/successes
+
+# torture_one - Does a single kvm.sh run.
+#
+# Usage:
+# torture_bootargs="[ kernel boot arguments ]"
+# torture_one flavor [ kvm.sh arguments ]
+#
+# Note that "flavor" is an arbitrary string. Supply --torture if needed.
+# Note that quoting is problematic. So on the command line, pass multiple
+# values with multiple kvm.sh argument instances.
+function torture_one {
+ local cur_bootargs=
+ local boottag=
+
+ echo " --- $curflavor:" Start `date` | tee -a $T/log
+ if test -n "$torture_bootargs"
+ then
+ boottag="--bootargs"
+ cur_bootargs="$torture_bootargs"
+ fi
+ "$@" $boottag "$cur_bootargs" --datestamp "$ds/results-$curflavor" > $T/$curflavor.out 2>&1
+ retcode=$?
+ resdir="`grep '^Results directory: ' $T/$curflavor.out | tail -1 | sed -e 's/^Results directory: //'`"
+ if test -z "$resdir"
+ then
+ cat $T/$curflavor.out | tee -a $T/log
+ echo retcode=$retcode | tee -a $T/log
+ fi
+ if test "$retcode" == 0
+ then
+ echo "$curflavor($retcode)" $resdir >> $T/successes
+ else
+ echo "$curflavor($retcode)" $resdir >> $T/failures
+ fi
+}
+
+# torture_set - Does a set of tortures with and without KASAN and KCSAN.
+#
+# Usage:
+# torture_bootargs="[ kernel boot arguments ]"
+# torture_set flavor [ kvm.sh arguments ]
+#
+# Note that "flavor" is an arbitrary string. Supply --torture if needed.
+# Note that quoting is problematic. So on the command line, pass multiple
+# values with multiple kvm.sh argument instances.
+function torture_set {
+ local cur_kcsan_kmake_args=
+ local kcsan_kmake_tag=
+ local flavor=$1
+ shift
+ curflavor=$flavor
+ torture_one "$@"
+ if test "$do_kasan" = "yes"
+ then
+ curflavor=${flavor}-kasan
+ torture_one "$@" --kasan
+ fi
+ if test "$do_kcsan" = "yes"
+ then
+ curflavor=${flavor}-kcsan
+ if test -n "$kcsan_kmake_args"
+ then
+ kcsan_kmake_tag="--kmake-args"
+ cur_kcsan_kmake_args="$kcsan_kmake_args"
+ fi
+ torture_one $* --kconfig "CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y" $kcsan_kmake_tag $cur_kcsan_kmake_args --kcsan
+ fi
+}
+
+# make allmodconfig
+if test "$do_allmodconfig" = "yes"
+then
+ echo " --- allmodconfig:" Start `date` | tee -a $T/log
+ amcdir="tools/testing/selftests/rcutorture/res/$ds/allmodconfig"
+ mkdir -p "$amcdir"
+ echo " --- make clean" > "$amcdir/Make.out" 2>&1
+ make -j$MAKE_ALLOTED_CPUS clean >> "$amcdir/Make.out" 2>&1
+ echo " --- make allmodconfig" >> "$amcdir/Make.out" 2>&1
+ make -j$MAKE_ALLOTED_CPUS allmodconfig >> "$amcdir/Make.out" 2>&1
+ echo " --- make " >> "$amcdir/Make.out" 2>&1
+ make -j$MAKE_ALLOTED_CPUS >> "$amcdir/Make.out" 2>&1
+ retcode="$?"
+ echo $retcode > "$amcdir/Make.exitcode"
+ if test "$retcode" == 0
+ then
+ echo "allmodconfig($retcode)" $amcdir >> $T/successes
+ else
+ echo "allmodconfig($retcode)" $amcdir >> $T/failures
+ fi
+fi
+
+# --torture rcu
+if test "$do_rcutorture" = "yes"
+then
+ torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000"
+ torture_set "rcutorture" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "$configs_rcutorture" --trust-make
+fi
+
+if test "$do_locktorture" = "yes"
+then
+ torture_bootargs="torture.disable_onoff_at_boot"
+ torture_set "locktorture" tools/testing/selftests/rcutorture/bin/kvm.sh --torture lock --allcpus --duration "$duration_locktorture" --configs "$configs_locktorture" --trust-make
+fi
+
+if test "$do_scftorture" = "yes"
+then
+ torture_bootargs="scftorture.nthreads=$HALF_ALLOTED_CPUS torture.disable_onoff_at_boot"
+ torture_set "scftorture" tools/testing/selftests/rcutorture/bin/kvm.sh --torture scf --allcpus --duration "$duration_scftorture" --configs "$configs_scftorture" --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --trust-make
+fi
+
+if test "$do_refscale" = yes
+then
+ primlist="`grep '\.name[ ]*=' kernel/rcu/refscale.c | sed -e 's/^[^"]*"//' -e 's/".*$//'`"
+else
+ primlist=
+fi
+for prim in $primlist
+do
+ torture_bootargs="refscale.scale_type="$prim" refscale.nreaders=$HALF_ALLOTED_CPUS refscale.loops=10000 refscale.holdoff=20 torture.disable_onoff_at_boot"
+ torture_set "refscale-$prim" tools/testing/selftests/rcutorture/bin/kvm.sh --torture refscale --allcpus --duration 5 --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --bootargs "verbose_batched=$VERBOSE_BATCH_CPUS torture.verbose_sleep_frequency=8 torture.verbose_sleep_duration=$VERBOSE_BATCH_CPUS" --trust-make
+done
+
+if test "$do_rcuscale" = yes
+then
+ primlist="`grep '\.name[ ]*=' kernel/rcu/rcuscale.c | sed -e 's/^[^"]*"//' -e 's/".*$//'`"
+else
+ primlist=
+fi
+for prim in $primlist
+do
+ torture_bootargs="rcuscale.scale_type="$prim" rcuscale.nwriters=$HALF_ALLOTED_CPUS rcuscale.holdoff=20 torture.disable_onoff_at_boot"
+ torture_set "rcuscale-$prim" tools/testing/selftests/rcutorture/bin/kvm.sh --torture rcuscale --allcpus --duration 5 --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --trust-make
+done
+
+if test "$do_kvfree" = "yes"
+then
+ torture_bootargs="rcuscale.kfree_rcu_test=1 rcuscale.kfree_nthreads=16 rcuscale.holdoff=20 rcuscale.kfree_loops=10000 torture.disable_onoff_at_boot"
+ torture_set "rcuscale-kvfree" tools/testing/selftests/rcutorture/bin/kvm.sh --torture rcuscale --allcpus --duration 10 --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --trust-make
+fi
+
+echo " --- " $scriptname $args
+echo " --- " Done `date` | tee -a $T/log
+ret=0
+nsuccesses=0
+echo SUCCESSES: | tee -a $T/log
+if test -s "$T/successes"
+then
+ cat "$T/successes" | tee -a $T/log
+ nsuccesses="`wc -l "$T/successes" | awk '{ print $1 }'`"
+fi
+nfailures=0
+echo FAILURES: | tee -a $T/log
+if test -s "$T/failures"
+then
+ cat "$T/failures" | tee -a $T/log
+ nfailures="`wc -l "$T/failures" | awk '{ print $1 }'`"
+ ret=2
+fi
+echo Started at $startdate, ended at `date`, duration `get_starttime_duration $starttime`. | tee -a $T/log
+echo Summary: Successes: $nsuccesses Failures: $nfailures. | tee -a $T/log
+tdir="`cat $T/successes $T/failures | head -1 | awk '{ print $NF }' | sed -e 's,/[^/]\+/*$,,'`"
+if test -n "$tdir" && test $compress_kasan_vmlinux -gt 0
+then
+ # KASAN vmlinux files can approach 1GB in size, so compress them.
+ echo Looking for KASAN files to compress: `date` > "$tdir/log-xz" 2>&1
+ find "$tdir" -type d -name '*-kasan' -print > $T/xz-todo
+ ncompresses=0
+ batchno=1
+ if test -s $T/xz-todo
+ then
+ echo Size before compressing: `du -sh $tdir | awk '{ print $1 }'` `date` 2>&1 | tee -a "$tdir/log-xz" | tee -a $T/log
+ for i in `cat $T/xz-todo`
+ do
+ echo Compressing vmlinux files in ${i}: `date` >> "$tdir/log-xz" 2>&1
+ for j in $i/*/vmlinux
+ do
+ xz "$j" >> "$tdir/log-xz" 2>&1 &
+ ncompresses=$((ncompresses+1))
+ if test $ncompresses -ge $compress_kasan_vmlinux
+ then
+ echo Waiting for batch $batchno of $ncompresses compressions `date` | tee -a "$tdir/log-xz" | tee -a $T/log
+ wait
+ ncompresses=0
+ batchno=$((batchno+1))
+ fi
+ done
+ done
+ if test $ncompresses -gt 0
+ then
+ echo Waiting for final batch $batchno of $ncompresses compressions `date` | tee -a "$tdir/log-xz" | tee -a $T/log
+ fi
+ wait
+ echo Size after compressing: `du -sh $tdir | awk '{ print $1 }'` `date` 2>&1 | tee -a "$tdir/log-xz" | tee -a $T/log
+ echo Total duration `get_starttime_duration $starttime`. | tee -a $T/log
+ else
+ echo No compression needed: `date` >> "$tdir/log-xz" 2>&1
+ fi
+fi
+if test -n "$tdir"
+then
+ cp $T/log "$tdir"
+fi
+exit $ret
rcutorture.torture_type=tasks-rude
+rcutree.use_softirq=0
rcutorture.torture_type=tasks
+rcutree.use_softirq=0
git.samba.org / sfrench / cifs-2.6.git / commitdiff