fsnotify: lock annotation for event replacement

/*

 * Caller damn well better be holding whatever mutex is protecting the

 * old_holder->event_list.

 * old_holder->event_list and the new_event must be a clean event which

 * cannot be found anywhere else in the kernel.

 */

int fsnotify_replace_event(struct fsnotify_event_holder *old_holder,

			   struct fsnotify_event *new_event)

{

	struct fsnotify_event *old_event = old_holder->event;

	struct fsnotify_event_holder *new_holder = NULL;

	struct fsnotify_event_holder *new_holder = &new_event->holder;

	enum event_spinlock_class {

		SPINLOCK_OLD,

		SPINLOCK_NEW,

	};

	/*

	 * There is one fsnotify_event_holder embedded inside each fsnotify_event.

	 * Check if we expect to be able to use that holder.  If not alloc a new

	 * holder.

	 * For the overflow event it's possible that something will use the in

	 * event holder before we get the lock so we may need to jump back and

	 * alloc a new holder, this can't happen for most events...

	 * if the new_event's embedded holder is in use someone

	 * screwed up and didn't give us a clean new event.

	 */

	if (!list_empty(&new_event->holder.event_list)) {

alloc_holder:

		new_holder = fsnotify_alloc_event_holder();

		if (!new_holder)

			return -ENOMEM;

	}

	spin_lock(&old_event->lock);

	spin_lock(&new_event->lock);

	BUG_ON(!list_empty(&new_holder->event_list));

	if (list_empty(&new_event->holder.event_list)) {

		if (unlikely(new_holder))

			fsnotify_destroy_event_holder(new_holder);

		new_holder = &new_event->holder;

	} else if (unlikely(!new_holder)) {

		/* between the time we checked above and got the lock the in

		 * event holder was used, go back and get a new one */

		spin_unlock(&new_event->lock);

		spin_unlock(&old_event->lock);

		goto alloc_holder;

	}

	spin_lock_nested(&old_event->lock, SPINLOCK_OLD);

	spin_lock_nested(&new_event->lock, SPINLOCK_NEW);

	new_holder->event = new_event;

	list_replace_init(&old_holder->event_list, &new_holder->event_list);