This is a note to let you know that I've just added the patch titled
sched/dl: Fix race in dl_task_timer()
to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-dl-fix-race-in-dl_task_timer.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 0f397f2c90ce68821ee864c2c53baafe78de765d Mon Sep 17 00:00:00 2001
From: Kirill Tkhai <tkhai@xxxxxxxxx>
Date: Tue, 20 May 2014 13:33:42 +0400
Subject: sched/dl: Fix race in dl_task_timer()
From: Kirill Tkhai <tkhai@xxxxxxxxx>
commit 0f397f2c90ce68821ee864c2c53baafe78de765d upstream.
Throttled task is still on rq, and it may be moved to other cpu
if user is playing with sched_setaffinity(). Therefore, unlocked
task_rq() access makes the race.
Juri Lelli reports he got this race when dl_bandwidth_enabled()
was not set.
Other thing, pointed by Peter Zijlstra:
"Now I suppose the problem can still actually happen when
you change the root domain and trigger a effective affinity
change that way".
To fix that we do the same as made in __task_rq_lock(). We do not
use __task_rq_lock() itself, because it has a useful lockdep check,
which is not correct in case of dl_task_timer(). We do not need
pi_lock locked here. This case is an exception (PeterZ):
"The only reason we don't strictly need ->pi_lock now is because
we're guaranteed to have p->state == TASK_RUNNING here and are
thus free of ttwu races".
Signed-off-by: Kirill Tkhai <tkhai@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/3056991400578422@xxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/deadline.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -490,9 +490,17 @@ static enum hrtimer_restart dl_task_time
struct sched_dl_entity,
dl_timer);
struct task_struct *p = dl_task_of(dl_se);
- struct rq *rq = task_rq(p);
+ struct rq *rq;
+again:
+ rq = task_rq(p);
raw_spin_lock(&rq->lock);
+ if (rq != task_rq(p)) {
+ /* Task was moved, retrying. */
+ raw_spin_unlock(&rq->lock);
+ goto again;
+ }
+
/*
* We need to take care of a possible races here. In fact, the
* task might have changed its scheduling policy to something
Patches currently in stable-queue which might be from tkhai@xxxxxxxxx are
queue-3.14/sched-dl-fix-race-in-dl_task_timer.patch
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