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Wed, 17 Dec 2025 14:30:57 -0800 (PST) Date: Wed, 17 Dec 2025 17:30:56 -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, Muchun Song , Qi Zheng Subject: Re: [PATCH v2 19/28] mm: workingset: prevent lruvec release in workingset_refault() Message-ID: References: <1b6ad26b5199b8134de37506b669ad4e3c0b6356.1765956026.git.zhengqi.arch@bytedance.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1b6ad26b5199b8134de37506b669ad4e3c0b6356.1765956026.git.zhengqi.arch@bytedance.com> On Wed, Dec 17, 2025 at 03:27:43PM +0800, Qi Zheng wrote: > From: Muchun Song > > In the near future, a folio will no longer pin its corresponding > memory cgroup. So an lruvec returned by folio_lruvec() could be > released without the rcu read lock or a reference to its memory > cgroup. > > In the current patch, the rcu read lock is employed to safeguard > against the release of the lruvec in workingset_refault(). > > This serves as a preparatory measure for the reparenting of the > LRU pages. > > Signed-off-by: Muchun Song > Signed-off-by: Qi Zheng > Reviewed-by: Harry Yoo > --- > mm/workingset.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/workingset.c b/mm/workingset.c > index 445fc634196d8..427ca1a5625e8 100644 > --- a/mm/workingset.c > +++ b/mm/workingset.c > @@ -560,11 +560,12 @@ void workingset_refault(struct folio *folio, void *shadow) > * locked to guarantee folio_memcg() stability throughout. > */ > nr = folio_nr_pages(folio); > + rcu_read_lock(); > lruvec = folio_lruvec(folio); > mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr); > > if (!workingset_test_recent(shadow, file, &workingset, true)) This might sleep. You have to get a reference here and unlock RCU.