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-rw-r--r--kernel/events/core.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f0128c5ff278..8f908f077935 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5384,6 +5384,7 @@ int perf_event_release_kernel(struct perf_event *event)
again:
mutex_lock(&event->child_mutex);
list_for_each_entry(child, &event->child_list, child_list) {
+ void *var = NULL;
/*
* Cannot change, child events are not migrated, see the
@@ -5424,11 +5425,23 @@ again:
* this can't be the last reference.
*/
put_event(event);
+ } else {
+ var = &ctx->refcount;
}
mutex_unlock(&event->child_mutex);
mutex_unlock(&ctx->mutex);
put_ctx(ctx);
+
+ if (var) {
+ /*
+ * If perf_event_free_task() has deleted all events from the
+ * ctx while the child_mutex got released above, make sure to
+ * notify about the preceding put_ctx().
+ */
+ smp_mb(); /* pairs with wait_var_event() */
+ wake_up_var(var);
+ }
goto again;
}
mutex_unlock(&event->child_mutex);