From: Jan Kara <jack@xxxxxxx> Subject: 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@xxxxxxx Reported-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> Signed-off-by: Jan Kara <jack@xxxxxxx> Reviewed-by: Lino Sanfilippo <LinoSanfilippo@xxxxxx> Cc: Eric Paris <eparis@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/notify/notification.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff -puN fs/notify/notification.c~fanotify-fix-possible-false-warning-when-freeing-events fs/notify/notification.c --- a/fs/notify/notification.c~fanotify-fix-possible-false-warning-when-freeing-events +++ a/fs/notify/notification.c @@ -74,8 +74,17 @@ void fsnotify_destroy_event(struct fsnot /* 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); } _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
