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[PATCH 3.14 30/37] perf: Cure event->pending_disable race

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

------------------

From: Peter Zijlstra <peterz@infradead.org>

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@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dvyukov@google.com
Cc: eranian@google.com
Cc: oleg@redhat.com
Cc: panand@redhat.com
Cc: sasha.levin@oracle.com
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20160224174948.040469884@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/events/core.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1400,14 +1400,14 @@ 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--;

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[PATCH 3.14 00/37] 3.14.67-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 04:30 +0200
  [PATCH 3.14 28/37] usb: renesas_usbhs: disable TX IRQ before starting TX DMAC transfer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 04:30 +0200
  [PATCH 3.14 09/37] net: jme: fix suspend/resume on JMC260 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 27/37] usb: renesas_usbhs: avoid NULL pointer derefernce in usbhsf_pkt_handler() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 04/37] ALSA: timer: Use mod_timer() for rearming the system timer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 20/37] ipv4: fix broadcast packets reception Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 24/37] ipv6: l2tp: fix a potential issue in l2tp_ip6_recv Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 30/37] perf: Cure event->pending_disable race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 11/37] ipv6: re-enable fragment header matching in ipv6_find_hdr Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 23/37] ipv4: l2tp: fix a potential issue in l2tp_ip_recv Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 06/37] drm/radeon: add a dpm quirk for sapphire Dual-X R7 370 2G D5 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  [PATCH 3.14 25/37] ip6_tunnel: set rtnl_link_ops before calling register_netdevice Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-18 05:50 +0200
  Re: [PATCH 3.14 00/37] 3.14.67-stable review Guenter Roeck <linux@roeck-us.net> - 2016-04-18 18:40 +0200
  Re: [PATCH 3.14 00/37] 3.14.67-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2016-04-18 18:40 +0200

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