events: Add note to update_event_times comment about holding ctx->lock

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1308861279-15216-1-git-send-email-emunson@mgebm.netSigned-off-by: Ingo Molnar <mingo@elte.hu>

kernel/events/core.c

@@ -748,6 +748,7 @@ static u64 perf_event_time(struct perf_event *event)
 
 /*
  * Update the total_time_enabled and total_time_running fields for a event.
+ * The caller of this function needs to hold the ctx->lock.
  */
 static void update_event_times(struct perf_event *event)
 {