Re: [PATCH 12/19] kernel: convert css_set.refcount from atomic_t to refcount_t

[Tejun Heo]

Hello,

On Mon, Feb 20, 2017 at 12:19:01PM +0200, Elena Reshetova wrote:
> @@ -134,10 +135,13 @@ static inline void put_css_set(struct css_set *cset)
>  	 * can see it. Similar to atomic_dec_and_lock(), but for an
>  	 * rwlock
>  	 */
> -	if (atomic_add_unless(&cset->refcount, -1, 1))
> +	spin_lock_irqsave(&css_set_lock, flags);
> +	if (refcount_read(&cset->refcount) != 1) {
> +		WARN_ON(refcount_dec_and_test(&cset->refcount));
> +		spin_unlock_irqrestore(&css_set_lock, flags);
>  		return;
> +	}

This isn't an equivalent conversion and should have been mentioned in
the patch description.  Hmm... and I'm not sure this is a good idea.
Can't we add the matching operation on refcount_t rather than adding
extra locking like this?

Thanks.

-- 
tejun