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t=1794480910; bh=hBBRka0fgdENvERIYsPzoLXmI7OdvHBhAV6rADe9TMQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=mVR6HgOg/ceImyZhmMvUyCD1gCi9KdMcx9kDP6BtyYopaWHif25AK0lFQXIz3PlLm zvj/wn+r8mOdfmobgmEkg1F5syvIhoNuPdQ0wq/7Bt4XHmUBfShWInqaA3hMM0qgAk bCf+ouF4iY6V9bVOC1ovlXEnT7k/BLwoWZoFLHA9hnQ8Yln0CfvmEvcWw3Uhd4/CQL R3wgbLkxrrOeBi8R+QVPPIlQ6OpYmhYd7Z2hIKu7PV5KakhWIHd6htoTsjaYROEZP6 1fsO3oSdzbA9kWGhJD8pLIphaoAQSehJAY1gwsvr18zimH2uEhz1LPhYVDHRsm92/Y ddIb4UYpAYEUg== Message-ID: <9d1fa2c1-7090-417f-adfc-0b128c37622e@kernel.org> Date: Thu, 12 Nov 2026 11:55:05 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] memcg: flush nr_charged_bytes when the obj stock trylock fails Content-Language: en-US To: Shakeel Butt , Andrew Morton Cc: Johannes Weiner , David Hildenbrand , Michal Hocko , Roman Gushchin , Muchun Song , Meta kernel team , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org References: <20261112013220.4064478-1-shakeel.butt@linux.dev> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0A96DA000A X-Stat-Signature: yfkma687n3dqwtagoizkq3wubpap8fzo X-Rspam-User: X-HE-Tag: 1794480910-84200 X-HE-Meta: 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 Vo+Eo+L+ Dcr4wADOEVjns9dcaUx7d6csiIZ9YbiprntLdr21Q5V8CvLiH8Pj7OOHH/Dsj4Wo0o5VP/BLZEOqAa/RRSp4Vw9d1sDgVWc1wWOQbRA2etIMlNAsmkorbO+WCESSxOWrNehm6HS9vSWzoApeVpDlSLeQN6vNoDyMEzGUqbVAr7tnEWWW24Bb1Z3AiAbeXUFg3Bg8Hz0Q1b5dTH8VHnu/NEdg70hStXpQlLsK2IBRX7yZwQhQHbtHnWmkret+5QNEFzDU4XbC9n/RccQv0El2g6KlXsvUrN/OyVBcruGXDWCzBJfTl36VojSMnp4P1XgdNtOVYv78C1z8OcVo= 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 11/12/26 02:32, 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 Acked-by: Vlastimil Babka (SUSE) > --- > mm/memcontrol.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index f5f567f7d4a9..091401cecf39 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3553,6 +3553,8 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, > int i, slot = -1, empty_slot = -1; > > if (!stock) { > + nr_bytes += atomic_read(&objcg->nr_charged_bytes) > + ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; > nr_pages = nr_bytes >> PAGE_SHIFT; > nr_bytes = nr_bytes & (PAGE_SIZE - 1); > atomic_add(nr_bytes, &objcg->nr_charged_bytes);