On Mon, May 20, 2019 at 04:59:16PM -0400, Waiman Long wrote: > With separate count and owner, there are timing windows where the two > values are inconsistent. That can cause problem when trying to figure > out the exact state of the rwsem. For instance, a RT task will stop > optimistic spinning if the lock is acquired by a writer but the owner > field isn't set yet. That can be solved by combining the count and > owner together in a single atomic value.
I just realized we can use cmpxchg_double() here (where available of course).