Re: [PATCH 4/6] locking/rwsem: Avoid deceiving lock spinners

Davidlohr Bueso
2015-01-29T23:15:45Z

On Thu, 2015-01-29 at 12:18 -0800, Jason Low wrote:
> /*
> - * We break out the loop above on need_resched() and when the
> - * owner changed, which is a sign for heavy contention. Return
> - * success only when lock->owner is NULL.
> + * We break out the loop above on either need_resched(), when
> + * the owner is not running, or when the lock owner changed.
> + * Return success only when the lock owner changed.
> */
> - return lock->owner == NULL;
> + return lock->owner != owner;
> }

Ideally we would refactor all this, along with getting rid of
owner_running() at some point. It no longer makes sense to split up
mutex_spin_on_owner() and we're doing duplicate owner checks. It would
also be simpler than having to guess why we broke out of the loop, for
example.