[GIT PULL] perf fix

[Ingo Molnar]

Linus,

Please pull the latest perf-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf-urgent-for-linus

 Thanks,

	Ingo

------------------>
Will Deacon (1):
      perf events: Fix ring_buffer_wakeup() brown paperbag bug


 kernel/events/core.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d3b9df5..58690af 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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();
 }
 
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