From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756776AbcBXRwz (ORCPT ); Wed, 24 Feb 2016 12:52:55 -0500 Received: from casper.infradead.org ([85.118.1.10]:35783 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753926AbcBXRwx (ORCPT ); Wed, 24 Feb 2016 12:52:53 -0500 Message-Id: <20160224174948.040469884@infradead.org> User-Agent: quilt/0.61-1 Date: Wed, 24 Feb 2016 18:45:46 +0100 From: Peter Zijlstra To: peterz@infradead.org, mingo@kernel.org, alexander.shishkin@linux.intel.com, eranian@google.com Cc: linux-kernel@vger.kernel.org, vince@deater.net, dvyukov@google.com, andi@firstfloor.org, jolsa@redhat.com, panand@redhat.com, sasha.levin@oracle.com, oleg@redhat.com Subject: [PATCH 07/12] perf: Cure event->pending_disable race References: <20160224174539.570749654@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=peterz-perf-more-fixes-9.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Because event_sched_out() checks event->pending_disable _before_ actually disabling the event, it can happen that the event fires after it checks but before it gets disabled. This would leave event->pending_disable set and the queued irq_work will try and process it. However, if the event trigger was during schedule(), the event might have been de-scheduled by the time the irq_work runs, and perf_event_disable_local() will fail. Fix this by checking event->pending_disable _after_ we call event->pmu->del(). This depends on the latter being a compiler barrier, such that the compiler does not lift the load and re-creates the problem. Reviewed-by: Alexander Shishkin Tested-by: Alexander Shishkin Signed-off-by: Peter Zijlstra (Intel) --- kernel/events/core.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1696,14 +1696,14 @@ event_sched_out(struct perf_event *event perf_pmu_disable(event->pmu); + event->tstamp_stopped = tstamp; + event->pmu->del(event, 0); + event->oncpu = -1; event->state = PERF_EVENT_STATE_INACTIVE; if (event->pending_disable) { event->pending_disable = 0; event->state = PERF_EVENT_STATE_OFF; } - event->tstamp_stopped = tstamp; - event->pmu->del(event, 0); - event->oncpu = -1; if (!is_software_event(event)) cpuctx->active_oncpu--;