This is a note to let you know that I've just added the patch titled
perf: Cure event->pending_disable race
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-cure-event-pending_disable-race.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 28a967c3a2f99fa3b5f762f25cb2a319d933571b Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed, 24 Feb 2016 18:45:46 +0100
Subject: perf: Cure event->pending_disable race
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: dvyukov@xxxxxxxxxx
Cc: eranian@xxxxxxxxxx
Cc: oleg@xxxxxxxxxx
Cc: panand@xxxxxxxxxx
Cc: sasha.levin@xxxxxxxxxx
Cc: vince@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20160224174948.040469884@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/events/core.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1580,14 +1580,14 @@ 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--;
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-4.4/perf-cure-event-pending_disable-race.patch
queue-4.4/perf-do-not-double-free.patch
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