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Thu, 12 Nov 2026 07:21:02 -0800 (PST) Received: from localhost ([2605:8600:200:14e3:365a:60ff:fe62:ff29]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-67c58a0f312sm7504466d50.19.2026.11.12.07.21.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Nov 2026 07:21:00 -0800 (PST) Date: Thu, 12 Nov 2026 10:21:00 -0500 From: Johannes Weiner To: Shakeel Butt Cc: Andrew Morton , David Hildenbrand , Michal Hocko , Roman Gushchin , Muchun Song , Vlastimil Babka , Meta kernel team , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org Subject: Re: [PATCH] memcg: flush nr_charged_bytes when the obj stock trylock fails Message-ID: References: <20261112013220.4064478-1-shakeel.butt@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261112013220.4064478-1-shakeel.butt@linux.dev> 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_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: gb4nnddmch4tnyhhfp56q4s4pq4nkzyf X-Rspamd-Queue-Id: DBCE8C0003 X-Rspam-User: X-HE-Tag: 1794497312-891914 X-HE-Meta: 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 z6fz3blv 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 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 Wed, Nov 11, 2026 at 05:32:20PM -0800, Shakeel Butt wrote: > When interrupt code, such as an RCU callback in softirq, runs on top of > a task that holds the obj stock lock, its trylock fails and the bytes go > to objcg->nr_charged_bytes. Nothing empties that counter while every CPU > using the objcg keeps it in its stock, so it can grow without limit. > > Users see memory.current and the "kernel" field of memory.stat keep > growing while the cgroup's real usage does not. With memory.high or > memory.max set, the cgroup is reclaimed, throttled or even OOM-killed > for memory it does not use. The counter is 32-bit, so after 4 GiB it > wraps, and those 4 GiB stay charged to the cgroup and its ancestors > until reboot, even after the cgroup is removed. > > Fix it by uncharging the whole pages in nr_charged_bytes whenever the > trylock fails. > > Fixes: 200577f69f29 ("memcg: objcg stock trylock without irq disabling") > Reported-by: Chris Mason > Signed-off-by: Shakeel Butt > Cc: stable@vger.kernel.org Reviewed-by: Johannes Weiner