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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-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261023222313.3979455-1-tjmercier@google.com> 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