Commit 0b1b8652 authored Oct 07, 2016 by Jan Kara Committed by Linus Torvalds Oct 07, 2016

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 <mszeredi@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc: Eric Paris <eparis@redhat.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 073f6552

fs/notify/notification.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -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... */
		/*
		* 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);
		}

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