linux-kernel - [PATCH cgroup/for-6.16-fixes] cgroup: avoid null de-ref in css_rstat

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Message-ID: <20250731192734.106214-1-inwardvessel@gmail.com>
Date: Thu, 31 Jul 2025 12:27:34 -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 cgroup/for-6.16-fixes] cgroup: avoid null de-ref in css_rstat_exit()

This function may be called asynchronously in scenarios where preceding
calls to css_rstat_init() have not completed. Return early in this case.

Signed-off-by: JP Kobryn <inwardvessel@...il.com>
Suggested-by: Michal Koutný <mkoutny@...e.com>
Fixes: 5da3bfa029d68 ("cgroup: use separate rstat trees for each subsystem")
Reported-by: syzbot+8d052e8b99e40bc625ed@...kaller.appspotmail.com
---
 kernel/cgroup/rstat.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index cbeaa499a96a..408e52d5f7a4 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -488,6 +488,9 @@ void css_rstat_exit(struct cgroup_subsys_state *css)
 	if (!css_uses_rstat(css))
 		return;
 
+	if (!css->rstat_cpu)
+		return;
+
 	css_rstat_flush(css);
 
 	/* sanity check */
-- 
2.47.3