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[109.81.20.177]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a35a30e11bsm232464125e9.1.2026.10.26.06.25.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Oct 2026 06:25:47 -0700 (PDT) Date: Mon, 26 Oct 2026 14:25:44 +0100 From: Michal Hocko To: "T.J. Mercier" Cc: hannes@cmpxchg.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, zhengqi.arch@bytedance.com, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm: memcontrol: fix NULL pointer deref in high_work_func() on dying memcg Message-ID: References: <20261023222313.3979455-1-tjmercier@google.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261023222313.3979455-1-tjmercier@google.com> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 0040D140002 X-Stat-Signature: gy789jczi6eqp9j94drfr1udufpbafni X-Rspam-User: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793021148-618582 X-HE-Meta: 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 TSBSNlpK dHFwK5LKGUdknsOX6duHZNKvvyWSTyOVz5xy8YtnJn7VeAZzJVyRKq8868N/k/mGg1sLnF26Thsq99CdSnZhiEa1tphpg1WEQj71HKDarIC63yO9KP/G/bWHiypgeXGsmUYlJGPl7wBHkeMQ2KuFxNAOjDSixiCWeiU+MTBAKDWhPk+/+RCpse9Kt+K0t1FM5/+dvyWoWxk2W+S6lXjHs7bCB/0cgt9p1BYLn0dKNkSCLvLd0DXx1guqBJIuV3FGFkhQen9tKTIsKL9oeusOFZ2d9mLFVJhl3FcsvXL6JYdDv798yDiciwSXt38pJuoQRMN1+3gPvszRZy5Mbs7Iq1OiG0zQLbfG9lW59sgovgKpDTOZ34A5LsTdz/2APCDhC3Apr3FMO6nYSOmq3T5yDrPlq6w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Fri 23-10-26 15:23:13, T.J. Mercier wrote: [...] > --- > mm/memcontrol.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index a05d9a8baa1b..84f4a8fd4d16 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2457,7 +2457,10 @@ static void high_work_func(struct work_struct *work) > struct mem_cgroup *memcg; > > memcg = container_of(work, struct mem_cgroup, high_work); > + if (!css_tryget_online(&memcg->css)) > + return; > reclaim_high(memcg, MEMCG_CHARGE_BATCH, GFP_KERNEL); > + css_put(&memcg->css); > } OK. > static void high_irq_work_func(struct irq_work *work) > @@ -4463,6 +4466,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) > > page_counter_set_min(&memcg->memory, 0); > page_counter_set_low(&memcg->memory, 0); > + page_counter_set_high(&memcg->memory, PAGE_COUNTER_MAX); > + page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX); > > zswap_memcg_offline_cleanup(memcg); Should we simply disable_work_sync when the memcg is going to be released instead (mem_cgroup_css_released)? That should both prevent the run reclaim_high during the memcg shut down and and also avoid plaing with limits to work around. -- Michal Hocko SUSE Labs