On 6/4/19 5:45 AM, Peter Zijlstra wrote: > 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).
Does the 2 doubles need to be 128-bit aligned to use cmpxchg_double()? I don't think we can guarantee that unless we explicitly set this alignment. Cheers, Longman
