Re: [PATCH v4 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED flag

[Matthew Wilcox]

On Tue, May 15, 2018 at 05:49:50PM -0400, Waiman Long wrote:
> @@ -357,11 +357,8 @@ static inline bool rwsem_can_spin_on_owner(struct 
> rw_semaphore *sem)
>  
>       rcu_read_lock();
>       owner = READ_ONCE(sem->owner);
> -     if (!rwsem_owner_is_writer(owner)) {
> -             /*
> -              * Don't spin if the rwsem is readers owned.
> -              */
> -             ret = !rwsem_owner_is_reader(owner);
> +     if (!owner || !is_rwsem_owner_spinnable(owner)) {
> +             ret = !owner;   /* !owner is spinnable */
>               goto done;
>       }

This is confusingly written.  I think you mean ...

        if (!owner)
                goto done;
        if (!is_rwsem_owner_spinnable(owner)) {
                ret = false;
                goto done;
        }