From: Muchun Song <songmuchun@bytedance.com>
Date: Thu, 5 Mar 2026 11:52:29 +0000 (+0800)
Subject: mm: memcontrol: prevent memory cgroup release in count_memcg_folio_events()
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=f995da5341c1854e59415c2c2c6f0b6406b498f2;p=thirdparty%2Fkernel%2Flinux.git

mm: memcontrol: prevent memory cgroup release in count_memcg_folio_events()

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 count_memcg_folio_events().

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

Link: https://lore.kernel.org/dea6aa0389367f7fd6b715c8837a2cf7506bd889.1772711148.git.zhengqi.arch@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Allen Pais <apais@linux.microsoft.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chen Ridong <chenridong@huawei.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Imran Khan <imran.f.khan@oracle.com>
Cc: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yosry Ahmed <yosry@kernel.org>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 4454f03a4acf..ef26ba087844 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -975,10 +975,15 @@ void count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
 static inline void count_memcg_folio_events(struct folio *folio,
 		enum vm_event_item idx, unsigned long nr)
 {
-	struct mem_cgroup *memcg = folio_memcg(folio);
+	struct mem_cgroup *memcg;
 
-	if (memcg)
-		count_memcg_events(memcg, idx, nr);
+	if (!folio_memcg_charged(folio))
+		return;
+
+	rcu_read_lock();
+	memcg = folio_memcg(folio);
+	count_memcg_events(memcg, idx, nr);
+	rcu_read_unlock();
 }
 
 static inline void count_memcg_events_mm(struct mm_struct *mm,