perf/core: Fix the unthrottle logic

Its possible to IOC_PERIOD while the event is throttled, this would
re-start the event and the next tick would then try to unthrottle it,
and find the event wasn't actually stopped anymore.

This would tickle a WARN in the x86-pmu code which isn't expecting to
start a !stopped event.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Alexander Shishkin <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 712570dddacd..d39477390415 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4210,6 +4210,14 @@ static void __perf_event_period(struct perf_event *event,
 	active = (event->state == PERF_EVENT_STATE_ACTIVE);
 	if (active) {
 		perf_pmu_disable(ctx->pmu);
+		/*
+		 * We could be throttled; unthrottle now to avoid the tick
+		 * trying to unthrottle while we already re-started the event.
+		 */
+		if (event->hw.interrupts == MAX_INTERRUPTS) {
+			event->hw.interrupts = 0;
+			perf_log_throttle(event, 1);
+		}
 		event->pmu->stop(event, PERF_EF_UPDATE);
 	}