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| author | Ben Segall <bsegall@google.com> | 2013-10-16 11:16:22 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2013-10-29 12:02:21 +0100 |
| commit | 927b54fccbf04207ec92f669dce6806848cbec7d (patch) | |
| tree | 4ee5a37f4796df9883c6beb9b7a91ca8c8534049 /kernel | |
| parent | db06e78cc13d70f10877e0557becc88ab3ad2be8 (diff) | |
| download | linux-927b54fccbf04207ec92f669dce6806848cbec7d.tar.gz linux-927b54fccbf04207ec92f669dce6806848cbec7d.tar.bz2 linux-927b54fccbf04207ec92f669dce6806848cbec7d.zip | |
sched: Fix hrtimer_cancel()/rq->lock deadlock
__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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/fair.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 897d97762d8a..f6308cb44d09 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -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) |