[ 3.5.y.z extended stable ] Patch "sched: Convert BUG_ON()s in try_to_wake_up_local() to" has been added to staging queue

[Luis Henriques]

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

    sched: Convert BUG_ON()s in try_to_wake_up_local() to

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

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

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 35019587c05736a2c1a0484af215e7a05810d5de Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj at kernel.org>
Date: Mon, 18 Mar 2013 12:22:34 -0700
Subject: [PATCH] sched: Convert BUG_ON()s in try_to_wake_up_local() to
 WARN_ON_ONCE()s

commit 383efcd00053ec40023010ce5034bd702e7ab373 upstream.

try_to_wake_up_local() should only be invoked to wake up another
task in the same runqueue and BUG_ON()s are used to enforce the
rule. Missing try_to_wake_up_local() can stall workqueue
execution but such stalls are likely to be finite either by
another work item being queued or the one blocked getting
unblocked.  There's no reason to trigger BUG while holding rq
lock crashing the whole system.

Convert BUG_ON()s in try_to_wake_up_local() to WARN_ON_ONCE()s.

Signed-off-by: Tejun Heo <tj at kernel.org>
Acked-by: Steven Rostedt <rostedt at goodmis.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Link: http://lkml.kernel.org/r/20130318192234.GD3042@htj.dyndns.org
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/sched/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3231df8..473cac3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1651,8 +1651,10 @@ static void try_to_wake_up_local(struct task_struct *p)
 {
 	struct rq *rq = task_rq(p);

-	BUG_ON(rq != this_rq());
-	BUG_ON(p == current);
+	if (WARN_ON_ONCE(rq != this_rq()) ||
+	    WARN_ON_ONCE(p == current))
+		return;
+
 	lockdep_assert_held(&rq->lock);

 	if (!raw_spin_trylock(&p->pi_lock)) {
--
1.8.1.2