From: Jan Kara Date: Fri, 7 Oct 2016 23:56:58 +0000 (-0700) Subject: fanotify: fix possible false warning when freeing events X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=0b1b86527df4b1f398266c23e926dd788925bb69;p=linux-beck.git fanotify: fix possible false warning when freeing events 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. Link: http://lkml.kernel.org/r/1473797711-14111-7-git-send-email-jack@suse.cz Reported-by: Miklos Szeredi Signed-off-by: Jan Kara Reviewed-by: Lino Sanfilippo Cc: Eric Paris Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/notify/notification.c b/fs/notify/notification.c index 8a7a8cd041e8..1a8010e7a2a0 100644 --- a/fs/notify/notification.c +++ b/fs/notify/notification.c @@ -74,8 +74,17 @@ 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); }