[PATCH] perf_events: fix NULL point in free_event()

[Stephane Eranian <eranian@google.com>]

Without the following patch, perf top as non-root and
paranoid cpu set causes a NULL pointer dereference in
free_event() because event->ctx is NULL.

free_event() may be called, on the error path, before
event->ctx is set.

Signed-off-by: Stephane Eranian <eranian@google.com>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index f29b525..a7d5e7a 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2150,7 +2150,8 @@ static void free_event(struct perf_event *event)
 	if (event->destroy)
 		event->destroy(event);
 
-	put_ctx(event->ctx);
+	if (event->ctx)
+		put_ctx(event->ctx);
 	call_rcu(&event->rcu_head, free_event_rcu);
 }