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perf events: Fix ring_buffer_wakeup() brown paperbag bug

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Commit 10c6db11 ("perf: Fix loss of notification with multi-event")
seems to unconditionally dereference event->rb in the wakeup handler,
this is wrong, there might not be a buffer attached.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111213152651.GP20297@mudshark.cambridge.arm.com
[ minor edits ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Will Deacon 2011-12-13 20:40:45 +01:00 committed by Ingo Molnar
parent 373da0a2a3
commit 44b7f4b98d
1 changed files with 6 additions and 2 deletions
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8
kernel/events/core.c
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@ -3558,9 +3558,13 @@ static void ring_buffer_wakeup(struct perf_event *event)
rcu_read_lock();
rb = rcu_dereference(event->rb);
list_for_each_entry_rcu(event, &rb->event_list, rb_entry) {
if (!rb)
goto unlock;
list_for_each_entry_rcu(event, &rb->event_list, rb_entry)
wake_up_all(&event->waitq);
}
unlock:
rcu_read_unlock();
}