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b=BZKlad+FQFaJnrsAKYEbygGXQNLKDbYqZXaYDEQKe+02JfQPkL81VfHswVMEapP2D 6yZ2LeH/m4bbfY3AYe7X/h+lYVLxNeViVA/JEXK8jr8q7aKkwui2g0rG+IzS844m5m T4BoTh0d40xZcq0g88AaK6G/nez3laDJOtRJ0iRk= Date: Sun, 22 Mar 2026 15:34:58 -0700 From: Andrew Morton To: David Carlier Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Qi Zheng , linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/memcontrol: fix obj_cgroup leak in mem_cgroup_css_online() error path Message-Id: <20260322153458.245cf0eae46bf8f57d6fe4ce@linux-foundation.org> In-Reply-To: <20260322193631.45457-1-devnexen@gmail.com> References: <20260322080142.5834-1-devnexen@gmail.com> <20260322193631.45457-1-devnexen@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1680618000E X-Stat-Signature: mx58q59wwch74dyqkw5hezrh3oqghpsz X-Rspam-User: X-HE-Tag: 1774218900-355937 X-HE-Meta: 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 H15r7cGu s0ObyynZljsPCVHeneBb2cy2l7zDYQYqXgXQZg3t6xoJ82jrU2GlOCJhpoVuFNVXGs1FAiTjPs0jhbuZmYDsfC4G0S084Dm2wYzGBQHXPVgeWJzbxQvvOpVqIkeygfMg71qGj212hpOoOhugYHwFdHHKbVWOn/+/bNB9PUWX11/OPfrvY0C4CsgQMgpkUJSlnzZAkg904EJ8e634dNr6Rqy7Ly5cVc1NpzVEH3ouo3JWxlY1HyDpsqfAF2b1bihmZTOr+1WJPtYVx9d9xk1gIFY6jWDn6BAkiyMIxlHhVqFE/w/Dac5s53wNF897OoaayJghBp92P7py3QJkvBIffJcevyA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 22 Mar 2026 19:36:31 +0000 David Carlier wrote: > When obj_cgroup_alloc() fails partway through the NUMA node loop in > mem_cgroup_css_online(), the free_objcg error path drops the extra > reference held by pn->orig_objcg but never kills the initial percpu_ref > from obj_cgroup_alloc() stored in pn->objcg. > > Since css_offline is never called when css_online fails, > memcg_reparent_objcgs() never runs, so the percpu_ref_kill() that > normally drops this initial reference never executes. The obj_cgroup and > its per-cpu ref allocations are leaked. > > Clear pn->objcg via rcu_replace_pointer() and add the missing > percpu_ref_kill() in the error path, matching the normal teardown > sequence in memcg_reparent_objcgs(). > > Also add a NULL check for pn in __mem_cgroup_free() to prevent a NULL > pointer dereference when alloc_mem_cgroup_per_node_info() fails partway > through the node loop in mem_cgroup_alloc(). Cool. > Fixes: 098fad3e1621 ("mm: memcontrol: convert objcg to be per-memcg per-node type") This is presently in mm.git's mm-unstable branch, not in mainline. > Cc: stable@vger.kernel.org So the cc:stable is inappropriate.