This is a note to let you know that I've just added the patch titled
sched: Fix hrtimer_cancel()/rq->lock deadlock
to the 3.12-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-fix-hrtimer_cancel-rq-lock-deadlock.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 927b54fccbf04207ec92f669dce6806848cbec7d Mon Sep 17 00:00:00 2001
From: Ben Segall <bsegall@xxxxxxxxxx>
Date: Wed, 16 Oct 2013 11:16:22 -0700
Subject: sched: Fix hrtimer_cancel()/rq->lock deadlock
From: Ben Segall <bsegall@xxxxxxxxxx>
commit 927b54fccbf04207ec92f669dce6806848cbec7d upstream.
__start_cfs_bandwidth calls hrtimer_cancel while holding rq->lock,
waiting for the hrtimer to finish. However, if sched_cfs_period_timer
runs for another loop iteration, the hrtimer can attempt to take
rq->lock, resulting in deadlock.
Fix this by ensuring that cfs_b->timer_active is cleared only if the
_latest_ call to do_sched_cfs_period_timer is returning as idle. Then
__start_cfs_bandwidth can just call hrtimer_try_to_cancel and wait for
that to succeed or timer_active == 1.
Signed-off-by: Ben Segall <bsegall@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: pjt@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20131016181622.22647.16643.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Chris J Arges <chris.j.arges@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/fair.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2459,6 +2459,13 @@ static int do_sched_cfs_period_timer(str
if (idle)
goto out_unlock;
+ /*
+ * if we have relooped after returning idle once, we need to update our
+ * status as actually running, so that other cpus doing
+ * __start_cfs_bandwidth will stop trying to cancel us.
+ */
+ cfs_b->timer_active = 1;
+
__refill_cfs_bandwidth_runtime(cfs_b);
if (!throttled) {
@@ -2727,11 +2734,11 @@ void __start_cfs_bandwidth(struct cfs_ba
* (timer_active==0 becomes visible before the hrtimer call-back
* terminates). In either case we ensure that it's re-programmed
*/
- while (unlikely(hrtimer_active(&cfs_b->period_timer))) {
+ while (unlikely(hrtimer_active(&cfs_b->period_timer)) &&
+ hrtimer_try_to_cancel(&cfs_b->period_timer) < 0) {
+ /* bounce the lock to allow do_sched_cfs_period_timer to run */
raw_spin_unlock(&cfs_b->lock);
- /* ensure cfs_b->lock is available while we wait */
- hrtimer_cancel(&cfs_b->period_timer);
-
+ cpu_relax();
raw_spin_lock(&cfs_b->lock);
/* if someone else restarted the timer then we're done */
if (cfs_b->timer_active)
Patches currently in stable-queue which might be from bsegall@xxxxxxxxxx are
queue-3.12/sched-fix-hrtimer_cancel-rq-lock-deadlock.patch
queue-3.12/sched-fix-cfs_bandwidth-misuse-of-hrtimer_expires_remaining.patch
queue-3.12/sched-fix-race-on-toggling-cfs_bandwidth_used.patch
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