Lockable itself isn't distributed (or, at the very least, doesn't appear distributed from the outside), so I'm not sure if linearizability applies here, but maybe I'm misunderstanding you comment.

In a similar vein, I guess you can ask what happens if a client first checks if a lock is available then tries to acquire it, in two separate steps; but in that case, there's no guarantee that the lock wasn't acquired in between checking and acquisition.