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perf: Cure event->pending_disable race
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>
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@ -1696,14 +1696,14 @@ event_sched_out(struct perf_event *event,
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perf_pmu_disable(event->pmu);
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event->tstamp_stopped = tstamp;
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event->pmu->del(event, 0);
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event->oncpu = -1;
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event->state = PERF_EVENT_STATE_INACTIVE;
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if (event->pending_disable) {
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event->pending_disable = 0;
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event->state = PERF_EVENT_STATE_OFF;
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}
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event->tstamp_stopped = tstamp;
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event->pmu->del(event, 0);
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event->oncpu = -1;
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if (!is_software_event(event))
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cpuctx->active_oncpu--;
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