If the header object gets deleted (perhaps along with the entire pool),
there is no point in attempting to reregister the watch.  Treat this
the same as blacklisting: fail all pending and new I/Os requiring the
lock.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
        ret = __rbd_register_watch(rbd_dev);
        if (ret) {
                rbd_warn(rbd_dev, "failed to reregister watch: %d", ret);
-               if (ret == -EBLACKLISTED) {
+               if (ret == -EBLACKLISTED || ret == -ENOENT) {
                        set_bit(RBD_DEV_FLAG_BLACKLISTED, &rbd_dev->flags);
                        need_to_wake = true;
                } else {