linux-kernel - Re: [PATCH] sched: remove false-positive warning from wake_up

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Message-ID: <20151203123650.GZ3816@twins.programming.kicks-ass.net>
Date:	Thu, 3 Dec 2015 13:36:50 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org, oleg@...hat.com,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] sched: remove false-positive warning from
 wake_up_process()

On Mon, Nov 30, 2015 at 08:34:20PM -0500, Sasha Levin wrote:
> Futex can have a spurious wake up before we actually wake it up on our own,
> which will trigger this warning if the task is still stopped.

I've edited the changelog like so, please let me know if that is fine
with you.

Thanks.

---
Subject: sched: Remove false-positive warning from wake_up_process()
From: Sasha Levin <sasha.levin@...cle.com>
Date: Mon, 30 Nov 2015 20:34:20 -0500

Because wakeups can (fundamentally) be late, a task might not be in
the expected state. Therefore testing against a task's state is racy,
and can yield false positives.

Fixes: 9067ac85d533 ("wake_up_process() should be never used to wakeup a TASK_STOPPED/TRACED task")
Cc: oleg@...hat.com
Cc: torvalds@...ux-foundation.org
Cc: mingo@...hat.com
Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: http://lkml.kernel.org/r/1448933660-23082-1-git-send-email-sasha.levin@oracle.com
---
 kernel/sched/core.c |    1 -
 1 file changed, 1 deletion(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2160,7 +2160,6 @@ static void try_to_wake_up_local(struct
  */
 int wake_up_process(struct task_struct *p)
 {
-	WARN_ON(task_is_stopped_or_traced(p));
 	return try_to_wake_up(p, TASK_NORMAL, 0);
 }
 EXPORT_SYMBOL(wake_up_process);
--
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