+.. SPDX-License-Identifier: GPL-2.0
+
+========================
RCU and lockdep checking
+========================
All flavors of RCU have lockdep checking available, so that lockdep is
aware of when each task enters and leaves any flavor of RCU read-side
deadlocks and the like.
In addition, RCU provides the following primitives that check lockdep's
-state:
+state::
rcu_read_lock_held() for normal RCU.
rcu_read_lock_bh_held() for RCU-bh.
The rcu_dereference_check() check expression can be any boolean
expression, but would normally include a lockdep expression. However,
any boolean expression can be used. For a moderately ornate example,
-consider the following:
+consider the following::
file = rcu_dereference_check(fdt->fd[fd],
lockdep_is_held(&files->file_lock) ||
any change from taking place, and finally, in case (3) the current task
is the only task accessing the file_struct, again preventing any change
from taking place. If the above statement was invoked only from updater
-code, it could instead be written as follows:
+code, it could instead be written as follows::
file = rcu_dereference_protected(fdt->fd[fd],
lockdep_is_held(&files->file_lock) ||
For example, the workqueue for_each_pwq() macro is intended to be used
either within an RCU read-side critical section or with wq->mutex held.
-It is thus implemented as follows:
+It is thus implemented as follows::
#define for_each_pwq(pwq, wq)
list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,