sched/core: Fix preempt warning in ttwu

John reported a DEBUG_PREEMPT warning caused by commit:

  aacedf26fb76 ("sched/core: Optimize try_to_wake_up() for local wakeups")

I overlooked that ttwu_stat() requires preemption disabled.

Reported-by: John Stultz <john.stultz@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: aacedf26fb76 ("sched/core: Optimize try_to_wake_up() for local wakeups")
Link: https://lkml.kernel.org/r/20190710105736.GK3402@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fa43ce3962e7959f94ea17fed65de41c91d0d0a8..2b037f1954732ab5a3b5bca3ecc7bd4a638774bc 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2399,6 +2399,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
        unsigned long flags;
        int cpu, success = 0;
 
+       preempt_disable();
        if (p == current) {
                /*
                 * We're waking current, this means 'p->on_rq' and 'task_cpu(p)
@@ -2412,7 +2413,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
                 *    it disabling IRQs (this allows not taking ->pi_lock).
                 */
                if (!(p->state & state))
-                       return false;
+                       goto out;
 
                success = 1;
                cpu = task_cpu(p);
@@ -2526,6 +2527,7 @@ unlock:
 out:
        if (success)
                ttwu_stat(p, cpu, wake_flags);
+       preempt_enable();
 
        return success;
 }