[tip:sched/urgent] sched/core: Fix preempt warning in ttwu

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  e3d85487fba42206024bc3ed32e4b581c7cb46db
Gitweb:     https://git.kernel.org/tip/e3d85487fba42206024bc3ed32e4b581c7cb46db
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 10 Jul 2019 12:57:36 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 13 Jul 2019 11:23:27 +0200

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>
---
 kernel/sched/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fa43ce3962e7..2b037f195473 100644
--- 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;
 }