In rename, all objects involved but target may be remote, i.e. source, source parent, target parent may be remote object, herein to know whether source is a remote object on source parent, we need to compare which MDT they are located.

In mdt_getattr_name_lock(), if name is NULL, the LOOKUP lock can't be returned to client, because this object may be a remote object under its parent, and the remote LOOKUP lock is on the MDT where its parent is located.