linux-kernel - [PATCH v2 13/28] mm: migrate: prevent memory cgroup release in folio_migrate

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Message-ID: <1554459c705a46324b83799ede617b670b9e22fb.1765956025.git.zhengqi.arch@bytedance.com>
Date: Wed, 17 Dec 2025 15:27:37 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: hannes@...xchg.org,
	hughd@...gle.com,
	mhocko@...e.com,
	roman.gushchin@...ux.dev,
	shakeel.butt@...ux.dev,
	muchun.song@...ux.dev,
	david@...nel.org,
	lorenzo.stoakes@...cle.com,
	ziy@...dia.com,
	harry.yoo@...cle.com,
	imran.f.khan@...cle.com,
	kamalesh.babulal@...cle.com,
	axelrasmussen@...gle.com,
	yuanchu@...gle.com,
	weixugc@...gle.com,
	chenridong@...weicloud.com,
	mkoutny@...e.com,
	akpm@...ux-foundation.org,
	hamzamahfooz@...ux.microsoft.com,
	apais@...ux.microsoft.com,
	lance.yang@...ux.dev
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	Muchun Song <songmuchun@...edance.com>,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v2 13/28] mm: migrate: prevent memory cgroup release in folio_migrate_mapping()

From: Muchun Song <songmuchun@...edance.com>

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_migrate_mapping().

This serves as a preparatory measure for the reparenting of the
LRU pages.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
---
 mm/migrate.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index 5169f9717f606..8bcd588c083ca 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -671,6 +671,7 @@ static int __folio_migrate_mapping(struct address_space *mapping,
 		struct lruvec *old_lruvec, *new_lruvec;
 		struct mem_cgroup *memcg;
 
+		rcu_read_lock();
 		memcg = folio_memcg(folio);
 		old_lruvec = mem_cgroup_lruvec(memcg, oldzone->zone_pgdat);
 		new_lruvec = mem_cgroup_lruvec(memcg, newzone->zone_pgdat);
@@ -698,6 +699,7 @@ static int __folio_migrate_mapping(struct address_space *mapping,
 			mod_lruvec_state(new_lruvec, NR_FILE_DIRTY, nr);
 			__mod_zone_page_state(newzone, NR_ZONE_WRITE_PENDING, nr);
 		}
+		rcu_read_unlock();
 	}
 	local_irq_enable();
 
-- 
2.20.1