---

yaml
---
r: 191290
b: refs/heads/master
c: a0507c8
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: cce913178118b0b36742eb7544c2b38a0c957ee7
+refs/heads/master: a0507c84bf47dfd204299774f45fd16da33f0619

trunk/kernel/perf_event.c

@@ -1867,7 +1867,19 @@ int perf_event_release_kernel(struct perf_event *event)
 	event->state = PERF_EVENT_STATE_FREE;
 
 	WARN_ON_ONCE(ctx->parent_ctx);
-	mutex_lock(&ctx->mutex);
+	/*
+	 * There are two ways this annotation is useful:
+	 *
+	 *  1) there is a lock recursion from perf_event_exit_task
+	 *     see the comment there.
+	 *
+	 *  2) there is a lock-inversion with mmap_sem through
+	 *     perf_event_read_group(), which takes faults while
+	 *     holding ctx->mutex, however this is called after
+	 *     the last filedesc died, so there is no possibility
+	 *     to trigger the AB-BA case.
+	 */
+	mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING);
 	perf_event_remove_from_context(event);
 	mutex_unlock(&ctx->mutex);
 
@@ -5305,7 +5317,7 @@ void perf_event_exit_task(struct task_struct *child)
 	 *
 	 * But since its the parent context it won't be the same instance.
 	 */
-	mutex_lock_nested(&child_ctx->mutex, SINGLE_DEPTH_NESTING);
+	mutex_lock(&child_ctx->mutex);
 
 again:
 	list_for_each_entry_safe(child_event, tmp, &child_ctx->pinned_groups,