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;
	}