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From: Shakeel Butt To: Johannes Weiner Cc: Qi Zheng , hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, muchun.song@linux.dev, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chenridong@huaweicloud.com, mkoutny@suse.com, akpm@linux-foundation.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng Subject: Re: [PATCH v2 17/28] mm: thp: prevent memory cgroup release in folio_split_queue_lock{_irqsave}() Message-ID: References: <4cb81ea06298a3b41873b7086bfc68f64b2ba8be.1765956025.git.zhengqi.arch@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam02 X-Stat-Signature: n3ge3an7uqp3oym14sdfhkuue3518r6h X-Rspam-User: X-Rspamd-Queue-Id: CB4EE180004 X-HE-Tag: 1766193107-363374 X-HE-Meta: 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 2l3bDGKA QdC55z62Z40/RLcDfSuNP4qrQsAPjxx1JjMLL1qTvf6961xeq22NwtoMveMIk2JRlBUWLCJMfkIjdL9aX4Eeg6LnKema7YQ//8rrEs0M3Y8Dm9Sf+x+Zhu4hdx8/YOJEEdRK/8SB+NhV9vodHGYuEBuZWB/TdiW8J77q1c7vkVbto5jm6fNceKwDF2NFwDIz0mVY+SM6a//uM9w8FFI2PIZKnDR5h7tH15sOUvay59Y1COtmopumYwJMWwyQ9U9vBiK1hIxKFlflBs3DJr8tviG1eqPjC/a9IBkkIFC++QV5VcBY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Dec 17, 2025 at 05:27:17PM -0500, Johannes Weiner wrote: > On Wed, Dec 17, 2025 at 03:27:41PM +0800, Qi Zheng wrote: > > From: Qi Zheng > > > > In the near future, a folio will no longer pin its corresponding memory > > cgroup. To ensure safety, it will only be appropriate to hold the rcu read > > lock or acquire a reference to the memory cgroup returned by > > folio_memcg(), thereby preventing it from being released. > > > > In the current patch, the rcu read lock is employed to safeguard against > > the release of the memory cgroup in folio_split_queue_lock{_irqsave}(). > > > > Signed-off-by: Qi Zheng > > Reviewed-by: Harry Yoo > > --- > > mm/huge_memory.c | 16 ++++++++++++++-- > > 1 file changed, 14 insertions(+), 2 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 12b46215b30c1..b9e6855ec0b6a 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -1154,13 +1154,25 @@ split_queue_lock_irqsave(int nid, struct mem_cgroup *memcg, unsigned long *flags > > > > static struct deferred_split *folio_split_queue_lock(struct folio *folio) > > { > > - return split_queue_lock(folio_nid(folio), folio_memcg(folio)); > > + struct deferred_split *queue; > > + > > + rcu_read_lock(); > > + queue = split_queue_lock(folio_nid(folio), folio_memcg(folio)); > > + rcu_read_unlock(); > > Ah, the memcg destruction path is acquiring the split queue lock for > reparenting. Once you have it locked, it's safe to drop the rcu lock. Qi, please add the above explanation in a comment and with that: Acked-by: Shakeel Butt