When freeing permission events by fsnotify_destroy_event(), the warning
WARN_ON(!list_empty(&event->list));
may falsely hit. This is because although fanotify_get_response() saw
event->response set, there is nothing to make sure the current CPU also
sees the removal of the event from the list. Add proper locking around
the WARN_ON() to avoid the false warning.
Reported-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/notify/notification.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 070d255b24a2..6b7f430bb2de 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -73,8 +73,17 @@ void fsnotify_destroy_event(struct fsnotify_group *group,
/* Overflow events are per-group and we don't want to free them */
if (!event || event->mask == FS_Q_OVERFLOW)
return;
- /* If the event is still queued, we have a problem... */
- WARN_ON(!list_empty(&event->list));
+ /*
+ * If the event is still queued, we have a problem... Do an unreliable
+ * lockless check first to avoid locking in the common case. The
+ * locking may be necessary for permission events which got removed
+ * from the list by a different CPU than the one freeing the event.
+ */
+ if (!list_empty(&event->list)) {
+ spin_lock(&group->notification_lock);
+ WARN_ON(!list_empty(&event->list));
+ spin_unlock(&group->notification_lock);
+ }
group->ops->free_event(event);
}
--
2.6.6
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