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| author | Ben Segall <bsegall@google.com> | 2013-10-16 11:16:22 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-01-15 15:27:11 -0800 |
| commit | 03d35a39f4de9f2e9d7fbc5c2d03dbcc5b882df7 (patch) | |
| tree | be90a817103d24c521ba427819374fd0600cef40 | |
| parent | 9b318052acd24780f4dba1349ef3a30a7aef52ad (diff) | |
| download | lwn-03d35a39f4de9f2e9d7fbc5c2d03dbcc5b882df7.tar.gz lwn-03d35a39f4de9f2e9d7fbc5c2d03dbcc5b882df7.zip | |
sched: Fix hrtimer_cancel()/rq->lock deadlock
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@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>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -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 8609fa84210a..3ce6561109b7 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1771,6 +1771,13 @@ 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) { @@ -2043,11 +2050,11 @@ 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) |