linux-kernel - [PATCH 3.12 52/78] perf: Cure event->pending

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Message-Id: <3ea8a50be86da7690db5fd03ae3a3911773164ec.1461323133.git.jslaby@suse.cz>
Date:	Fri, 22 Apr 2016 13:05:35 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>, dvyukov@...gle.com,
	eranian@...gle.com, oleg@...hat.com, panand@...hat.com,
	sasha.levin@...cle.com, vince@...ter.net,
	Ingo Molnar <mingo@...nel.org>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 52/78] perf: Cure event->pending_disable race

From: Peter Zijlstra <peterz@...radead.org>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 28a967c3a2f99fa3b5f762f25cb2a319d933571b upstream.

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.

Tested-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: dvyukov@...gle.com
Cc: eranian@...gle.com
Cc: oleg@...hat.com
Cc: panand@...hat.com
Cc: sasha.levin@...cle.com
Cc: vince@...ter.net
Link: http://lkml.kernel.org/r/20160224174948.040469884@infradead.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 kernel/events/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index b9c4a60f5137..0b3c09a3f7b6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1389,14 +1389,14 @@ event_sched_out(struct perf_event *event,
 	if (event->state != PERF_EVENT_STATE_ACTIVE)
 		return;
 
+	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--;
-- 
2.8.1