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

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Message-Id: <20250826034022.1736249-2-chenridong@huaweicloud.com>
Date: Tue, 26 Aug 2025 03:40:20 +0000
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: [PATCH cgroup/for-next 1/3] cgroup: remove redundancy online_cnt

From: Chen Ridong <chenridong@...wei.com>

Both online_cnt and nr_descendants can indicate whether acitive
descendants exist. To make code simple, remove redundancy online_cnt,
use nr_descendants instead.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 include/linux/cgroup-defs.h |  6 ------
 kernel/cgroup/cgroup.c      | 13 ++++---------
 kernel/cgroup/debug.c       |  2 +-
 3 files changed, 5 insertions(+), 16 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 6b93a64115fe..d084c5c34c09 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -210,12 +210,6 @@ struct cgroup_subsys_state {
 	 */
 	u64 serial_nr;
 
-	/*
-	 * Incremented by online self and children.  Used to guarantee that
-	 * parents are not offlined before their children.
-	 */
-	atomic_t online_cnt;
-
 	/* percpu_ref killing and RCU release */
 	struct work_struct destroy_work;
 	struct rcu_work destroy_rwork;
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 79b1d79f86a3..5eb747a038f7 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5607,7 +5607,6 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
 	INIT_LIST_HEAD(&css->sibling);
 	INIT_LIST_HEAD(&css->children);
 	css->serial_nr = css_serial_nr_next++;
-	atomic_set(&css->online_cnt, 0);
 
 	if (cgroup_parent(cgrp)) {
 		css->parent = cgroup_css(cgroup_parent(cgrp), ss);
@@ -5631,12 +5630,8 @@ static int online_css(struct cgroup_subsys_state *css)
 		css->flags |= CSS_ONLINE;
 		rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
 
-		atomic_inc(&css->online_cnt);
-		if (css->parent) {
-			atomic_inc(&css->parent->online_cnt);
-			while ((css = css->parent))
-				css->nr_descendants++;
-		}
+		while ((css = css->parent))
+			css->nr_descendants++;
 	}
 	return ret;
 }
@@ -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);
 	}
diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index 80aa3f027ac3..fc2f3216173a 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -226,7 +226,7 @@ static int cgroup_subsys_states_read(struct seq_file *seq, void *v)
 				 css->parent->id);
 		seq_printf(seq, "%2d: %-4s\t- %p[%d] %d%s\n", ss->id, ss->name,
 			  css, css->id,
-			  atomic_read(&css->online_cnt), pbuf);
+			  css->nr_descendants, pbuf);
 	}
 
 	cgroup_kn_unlock(of->kn);
-- 
2.34.1