| From 927b54fccbf04207ec92f669dce6806848cbec7d Mon Sep 17 00:00:00 2001 |
| From: Ben Segall <bsegall@google.com> |
| Date: Wed, 16 Oct 2013 11:16:22 -0700 |
| Subject: sched: Fix hrtimer_cancel()/rq->lock deadlock |
| |
| From: Ben Segall <bsegall@google.com> |
| |
| 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> |
| |
| --- |
| kernel/sched/fair.c | 15 +++++++++++---- |
| 1 file changed, 11 insertions(+), 4 deletions(-) |
| |
| --- a/kernel/sched/fair.c |
| +++ b/kernel/sched/fair.c |
| @@ -1771,6 +1771,13 @@ 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) { |
| @@ -2043,11 +2050,11 @@ 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) |