Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761865Ab3JPSWx (ORCPT ); Wed, 16 Oct 2013 14:22:53 -0400 Received: from mail-oa0-f73.google.com ([209.85.219.73]:64590 "EHLO mail-oa0-f73.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761847Ab3JPSWu (ORCPT ); Wed, 16 Oct 2013 14:22:50 -0400 X-Greylist: delayed 387 seconds by postgrey-1.27 at vger.kernel.org; Wed, 16 Oct 2013 14:22:50 EDT Subject: [PATCH 3/5] sched: Fix hrtimer_cancel/rq->lock deadlock To: peterz@infradead.org, mingo@redhat.com From: Ben Segall Cc: pjt@google.com, linux-kernel@vger.kernel.org Date: Wed, 16 Oct 2013 11:16:22 -0700 Message-ID: <20131016181622.22647.16643.stgit@sword-of-the-dawn.mtv.corp.google.com> In-Reply-To: <20131016181548.22647.17161.stgit@sword-of-the-dawn.mtv.corp.google.com> References: <20131016181548.22647.17161.stgit@sword-of-the-dawn.mtv.corp.google.com> User-Agent: StGit/0.16 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2178 Lines: 55 __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 --- kernel/sched/fair.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index b0eba47..fc44cc3 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3234,6 +3234,13 @@ 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) { @@ -3502,11 +3509,11 @@ 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) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/