perf: Fix software event overflow

The below patch is for -stable only, upstream has a much larger patch
that contains the below hunk in commit a8b0ca17

Vince found that under certain circumstances software event overflows
go wrong and deadlock. Avoid trying to delete a timer from the timer
callback.
Reported-by: Vince Weaver <vweaver1@eecs.utk.edu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

kernel/events/core.c

@@ -5016,11 +5016,8 @@ static int __perf_event_overflow(struct perf_event *event, int nmi,
 	if (events && atomic_dec_and_test(&event->event_limit)) {
 		ret = 1;
 		event->pending_kill = POLL_HUP;
-		if (nmi) {
 		event->pending_disable = 1;
 		irq_work_queue(&event->pending);
-		} else
-			perf_event_disable(event);
 	}
 
 	if (event->overflow_handler)