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Fri, 29 May 2026 19:38:03 -0700 (PDT) Date: Sat, 30 May 2026 02:38:02 +0000 From: Wei Yang To: Johannes Weiner Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Shakeel Butt , Michal Hocko , Dave Chinner , Roman Gushchin , Muchun Song , Qi Zheng , Yosry Ahmed , Zi Yan , "Liam R . Howlett" , Usama Arif , Kiryl Shutsemau , Vlastimil Babka , Kairui Song , Mikhail Zaslonko , Vasily Gorbik , Baolin Wang , Barry Song , Dev Jain , Lance Yang , Nico Pache , Ryan Roberts , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/9] mm: list_lru: fix set_shrinker_bit() call during race with cgroup deletion Message-ID: <20260530023802.l5f6ywulxl2bpafg@master> Reply-To: Wei Yang References: <20260527204757.2544958-1-hannes@cmpxchg.org> <20260527204757.2544958-2-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260527204757.2544958-2-hannes@cmpxchg.org> User-Agent: NeoMutt/20170113 (1.7.2) X-Stat-Signature: eee86ik9ksqcnwfih5zkzpnw8trs8ga4 X-Rspamd-Queue-Id: E0E8FC000D X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1780108686-67663 X-HE-Meta: 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 Ng9BI+1l 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 27, 2026 at 04:45:08PM -0400, Johannes Weiner wrote: >When list_lru_add() races with cgroup deletion, the shrinker bit is set >on the wrong group and lost. This can cause a shrinker run to miss the >cgroup that actually has the object. > >When the passed in memcg is dead, the function finds the first non-dead >parent from the passed in memcg and adds the object there; but the >shrinker bit is set on the memcg that was passed in. > This means we just miss to reclaim some obj, but won't crash the kernel. >This bug is as old as the shrinker bitmap itself. > >Fix it by returning the "effective" memcg from the locking function, and >have the caller use that. > >Fixes: fae91d6d8be5 ("mm/list_lru.c: set bit in memcg shrinker bitmap on first list_lru item appearance") >Reported-by: Usama Arif >Reported-by: Sashiko >Signed-off-by: Johannes Weiner So we don't want to cc stable, right? The fix looks right, so Reviewed-by: Wei Yang -- Wei Yang Help you, Help me