sched: Fix hrtimer_cancel()/rq->lock deadlock (927b54fc) · Commits · 戴 / test

__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>

kernel/sched/fair.c

+11 −4

Original line number	Diff line number	Diff line
		@@ -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)

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