[4.2.y-ckt stable] Patch "sched/core: Remove false-positive warning from wake_up_process()" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    sched/core: Remove false-positive warning from wake_up_process()

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 026bffe7be89a26bf6b50195d1185264bd35d68e Mon Sep 17 00:00:00 2001
From: Sasha Levin <sasha.levin at oracle.com>
Date: Mon, 30 Nov 2015 20:34:20 -0500
Subject: sched/core: Remove false-positive warning from wake_up_process()

commit 119d6f6a3be8b424b200dcee56e74484d5445f7e upstream.

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.

Signed-off-by: Sasha Levin <sasha.levin at oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Acked-by: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Mike Galbraith <efault at gmx.de>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: oleg at redhat.com
Fixes: 9067ac85d533 ("wake_up_process() should be never used to wakeup a TASK_STOPPED/TRACED task")
Link: http://lkml.kernel.org/r/1448933660-23082-1-git-send-email-sasha.levin@oracle.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/sched/core.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 87c3bb8..99cc1f4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1972,7 +1972,6 @@ out:
  */
 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);
--
1.9.1