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sched: Fix hrtimer_cancel()/rq->lock deadlock

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__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@google.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: pjt@google.com
Link: http://lkml.kernel.org/r/20131016181622.22647.16643.stgit@sword-of-the-dawn.mtv.corp.google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ben Segall 2013-10-16 11:16:22 -07:00 committed by Ingo Molnar
parent db06e78cc1
commit 927b54fccb
1 changed files with 11 additions and 4 deletions
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15
kernel/sched/fair.c
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@ -3225,6 +3225,13 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
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) {
@ -3493,11 +3500,11 @@ void __start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
* (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)