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Wed, 17 Dec 2025 14:27:19 -0800 (PST) Received: from localhost ([2603:7000:c01:2716:929a:4aff:fe16:c778]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8beeba2cd7csm37904385a.29.2025.12.17.14.27.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Dec 2025 14:27:18 -0800 (PST) Date: Wed, 17 Dec 2025 17:27:17 -0500 From: Johannes Weiner To: Qi Zheng Cc: hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@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: <4cb81ea06298a3b41873b7086bfc68f64b2ba8be.1765956025.git.zhengqi.arch@bytedance.com> X-Rspam-User: X-Rspamd-Queue-Id: 85D6D1C0019 X-Rspamd-Server: rspam10 X-Stat-Signature: xtsxydqqnbqq9316wx6tex9oexikz8km X-HE-Tag: 1766010440-990245 X-HE-Meta: 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 nXnkWJYX 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 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 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. Acked-by: Johannes Weiner