rcu: Fixup noinstr warnings

A KCSAN build revealed we have explicit annoations through atomic_*()
usage, switch to arch_atomic_*() for the respective functions.

vmlinux.o: warning: objtool: rcu_nmi_exit()+0x4d: call to __kcsan_check_access() leaves .noinstr.text section
vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x25: call to __kcsan_check_access() leaves .noinstr.text section
vmlinux.o: warning: objtool: rcu_nmi_enter()+0x4f: call to __kcsan_check_access() leaves .noinstr.text section
vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0x2a: call to __kcsan_check_access() leaves .noinstr.text section
vmlinux.o: warning: objtool: __rcu_is_watching()+0x25: call to __kcsan_check_access() leaves .noinstr.text section

Additionally, without the NOP in instrumentation_begin(), objtool would
not detect the lack of the 'else instrumentation_begin();' branch in
rcu_nmi_enter().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 30827f82ad62a6016c14cca79381aea9029be3ce..204e76856435c9241342c6c1276891542c662dec 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -123,7 +123,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #ifdef CONFIG_DEBUG_ENTRY
 /* Begin/end of an instrumentation safe region */
 #define instrumentation_begin() ({                                     \
-       asm volatile("%c0:\n\t"                                         \
+       asm volatile("%c0: nop\n\t"                                             \
                     ".pushsection .discard.instr_begin\n\t"            \
                     ".long %c0b - .\n\t"                               \
                     ".popsection\n\t" : : "i" (__COUNTER__));          \

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c716eadc7617fe4c5181d687dcec9272e045f22e..6c6569e0586c55844337aa7dba7c7a38f7559597 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -250,7 +250,7 @@ static noinstr void rcu_dynticks_eqs_enter(void)
         * next idle sojourn.
         */
        rcu_dynticks_task_trace_enter();  // Before ->dynticks update!
-       seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
+       seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
        // RCU is no longer watching.  Better be in extended quiescent state!
        WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
                     (seq & RCU_DYNTICK_CTRL_CTR));
@@ -274,13 +274,13 @@ static noinstr void rcu_dynticks_eqs_exit(void)
         * and we also must force ordering with the next RCU read-side
         * critical section.
         */
-       seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
+       seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
        // RCU is now watching.  Better not be in an extended quiescent state!
        rcu_dynticks_task_trace_exit();  // After ->dynticks update!
        WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
                     !(seq & RCU_DYNTICK_CTRL_CTR));
        if (seq & RCU_DYNTICK_CTRL_MASK) {
-               atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
+               arch_atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
                smp_mb__after_atomic(); /* _exit after clearing mask. */
        }
 }
@@ -313,7 +313,7 @@ static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
 {
        struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
-       return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
+       return !(arch_atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
 }
 
 /*
@@ -633,6 +633,10 @@ static noinstr void rcu_eqs_enter(bool user)
        do_nocb_deferred_wakeup(rdp);
        rcu_prepare_for_idle();
        rcu_preempt_deferred_qs(current);
+
+       // instrumentation for the noinstr rcu_dynticks_eqs_enter()
+       instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
+
        instrumentation_end();
        WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
        // RCU is watching here ...
@@ -692,6 +696,7 @@ noinstr void rcu_nmi_exit(void)
 {
        struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
+       instrumentation_begin();
        /*
         * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
         * (We are exiting an NMI handler, so RCU better be paying attention
@@ -705,7 +710,6 @@ noinstr void rcu_nmi_exit(void)
         * leave it in non-RCU-idle state.
         */
        if (rdp->dynticks_nmi_nesting != 1) {
-               instrumentation_begin();
                trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
                                  atomic_read(&rdp->dynticks));
                WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
@@ -714,13 +718,15 @@ noinstr void rcu_nmi_exit(void)
                return;
        }
 
-       instrumentation_begin();
        /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
        trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
        WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
 
        if (!in_nmi())
                rcu_prepare_for_idle();
+
+       // instrumentation for the noinstr rcu_dynticks_eqs_enter()
+       instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
        instrumentation_end();
 
        // RCU is watching here ...
@@ -838,6 +844,10 @@ static void noinstr rcu_eqs_exit(bool user)
        rcu_dynticks_eqs_exit();
        // ... but is watching here.
        instrumentation_begin();
+
+       // instrumentation for the noinstr rcu_dynticks_eqs_exit()
+       instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
+
        rcu_cleanup_after_idle();
        trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks));
        WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
@@ -983,13 +993,21 @@ noinstr void rcu_nmi_enter(void)
                if (!in_nmi())
                        rcu_cleanup_after_idle();
 
+               instrumentation_begin();
+               // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
+               instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks));
+               // instrumentation for the noinstr rcu_dynticks_eqs_exit()
+               instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
+
                incby = 1;
        } else if (!in_nmi()) {
                instrumentation_begin();
                rcu_irq_enter_check_tick();
                instrumentation_end();
+       } else  {
+               instrumentation_begin();
        }
-       instrumentation_begin();
+
        trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
                          rdp->dynticks_nmi_nesting,
                          rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));