Re: [BUG]locking/rwsem: only clean RWSEM_FLAG_HANDOFF when already set

[Waiman Long]

On 11/11/21 14:36, Waiman Long wrote:
> On 11/11/21 14:20, Peter Zijlstra wrote:
> > On Thu, Nov 11, 2021 at 02:14:48PM -0500, Waiman Long wrote:
> > > As for the PHASE_CHANGE name, we have to be consistent in both rwsem 
> > > and
> > > mutex. Maybe a follow up patch if you think we should change the
> > > terminology.
> > Well, that's exactly the point, they do radically different things.
> > Having the same name for two different things is confusing.
> >
> > Anyway, let me go read that patch you sent.
>
> My understanding of handoff is to disable optimistic spinning to let 
> waiters in the wait queue have an opportunity to acquire the lock. 
> There are difference in details on how to do that in mutex and rwsem, 
> though.
>
> BTW, I have decided that we should further simply the trylock for loop 
> in rwsem_down_write_slowpath() to make it easier to read. That is the 
> only difference in the attached v2 patch compared with the previous one.

My bad, I forgot to initialize waiter.handoff_set in 
rwsem_down_write_slowpath(). I will send out an updated version once you 
have finished your review.

Cheers,
Longman