# Re: \[PATCH 12/19\] kernel: convert css\_set.refcount from atomic\_t to refcount\_t

- From: Tejun Heo \<hidden\>
- Date: 2017-03-06 19:54:42 
- List: cgroups
- Page: https://ratatoskr.run/cgroups/2017/03/119151
- Thread: https://ratatoskr.run/cgroups/2017/02/117691/t.md

```text
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
```