linux-kernel - Re: [PATCH cgroup/for-next 1/3] cgroup: remove redundancy online

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Message-ID: <50e7e538-3f97-4db7-accf-635f3c0daff9@huaweicloud.com>
Date: Wed, 27 Aug 2025 08:59:10 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: tj@...nel.org, hannes@...xchg.org, mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH cgroup/for-next 1/3] cgroup: remove redundancy online_cnt



On 2025/8/26 11:40, Chen Ridong wrote:

> @@ -5949,7 +5944,7 @@ static void css_killed_work_fn(struct work_struct *work)
>  		css_put(css);
>  		/* @css can't go away while we're holding cgroup_mutex */
>  		css = css->parent;
> -	} while (css && atomic_dec_and_test(&css->online_cnt));
> +	} while (css && css_is_dying(css) && !css->nr_descendants);
>  
>  	cgroup_unlock();
>  }
> @@ -5960,7 +5955,7 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
>  	struct cgroup_subsys_state *css =
>  		container_of(ref, struct cgroup_subsys_state, refcnt);
>  
> -	if (atomic_dec_and_test(&css->online_cnt)) {
> +	if (!css->nr_descendants) {
>  		INIT_WORK(&css->destroy_work, css_killed_work_fn);
>  		queue_work(cgroup_offline_wq, &css->destroy_work);
>  	}

Hi Michal,

Thank you point out the data race issue, Can I modify the code just like:

@@ -5944,12 +5939,13 @@ static void css_killed_work_fn(struct work_struct *work)

        cgroup_lock();

-       do {
+       /* The CSS can only be taken offline when it has no living descendants. */
+       while (css && css_is_dying(css) && !css->nr_descendants) {
                offline_css(css);
                css_put(css);
                /* @css can't go away while we're holding cgroup_mutex */
                css = css->parent;
-       } while (css && atomic_dec_and_test(&css->online_cnt));
+       }

        cgroup_unlock();
 }
@@ -5960,10 +5956,9 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
        struct cgroup_subsys_state *css =
                container_of(ref, struct cgroup_subsys_state, refcnt);

-       if (atomic_dec_and_test(&css->online_cnt)) {
-               INIT_WORK(&css->destroy_work, css_killed_work_fn);
-               queue_work(cgroup_offline_wq, &css->destroy_work);
-       }
+       INIT_WORK(&css->destroy_work, css_killed_work_fn);
+       queue_work(cgroup_offline_wq, &css->destroy_work);
+
 }

-- 
Best regards,
Ridong