sched/core: Fix preempt warning in ttwu

John reported a DEBUG_PREEMPT warning caused by commit:

  aacedf2 ("sched/core: Optimize try_to_wake_up() for local wakeups")

I overlooked that ttwu_stat() requires preemption disabled.

Reported-by: John Stultz <[email protected]>
Tested-by: John Stultz <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: aacedf2 ("sched/core: Optimize try_to_wake_up() for local wakeups")
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: Peter Zijlstra

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 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 out:
 	if (success)
 		ttwu_stat(p, cpu, wake_flags);
+	preempt_enable();
 
 	return success;
 }