linux-kernel - [PATCH 4/5 cgroup/for-6.16-fixes] cgroup: initialize css rstat before linking to cgroups in css

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Message-ID: <20250722014030.297537-5-inwardvessel@gmail.com>
Date: Mon, 21 Jul 2025 18:40:29 -0700
From: JP Kobryn <inwardvessel@...il.com>
To: tj@...nel.org,
	shakeel.butt@...ux.dev,
	mkoutny@...e.com,
	yosryahmed@...gle.com,
	hannes@...xchg.org,
	akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	kernel-team@...a.com
Subject: [PATCH 4/5 cgroup/for-6.16-fixes] cgroup: initialize css rstat before linking to cgroups in css_create()

Calling css_rstat_init() after linking the css with its cgroup (and parent
cgroup) leaves the code vulnerable to async cleanup where css_rstat_exit()
is invoked on a fully initialized css. Avoid this by calling
css_rstat_init() before linking. The error can then be handled inline with
no async cleanup requirement.

Signed-off-by: JP Kobryn <inwardvessel@...il.com>
---
 kernel/cgroup/cgroup.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 1990c6113c7f..0f8c6ce21634 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5675,6 +5675,15 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 		return css;
 
 	init_css(css);
+
+	if (ss->css_rstat_flush) {
+		err = css_rstat_init(css);
+		if (err) {
+			ss->css_free(css);
+			goto err_out;
+		}
+	}
+
 	link_css(css, ss, cgrp);
 
 	err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
@@ -5686,12 +5695,6 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 		goto err_free_css;
 	css->id = err;
 
-	if (ss->css_rstat_flush) {
-		err = css_rstat_init(css);
-		if (err)
-			goto err_free_css;
-	}
-
 	/* @css is ready to be brought online now, make it visible */
 	list_add_tail_rcu(&css->sibling, &parent_css->children);
 	cgroup_idr_replace(&ss->css_idr, css, css->id);
@@ -5707,6 +5710,7 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 err_free_css:
 	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
 	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
+err_out:
 	return ERR_PTR(err);
 }
 
-- 
2.47.1