From: Muchun Song <songmuchun@bytedance.com>
Date: Thu, 5 Mar 2026 11:52:27 +0000 (+0800)
Subject: buffer: prevent memory cgroup release in folio_alloc_buffers()
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d10adce2c1a8ec61b46ff1841d3662f3c7a66d7a;p=thirdparty%2Fkernel%2Flinux.git

buffer: prevent memory cgroup release in folio_alloc_buffers()

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 function get_mem_cgroup_from_folio() is employed
to safeguard against the release of the memory cgroup.  This serves as a
preparatory measure for the reparenting of the LRU pages.

Link: https://lore.kernel.org/d6d48fdcf329c549373ac0a1c80fd9f38067e34e.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/fs/buffer.c b/fs/buffer.c
index f3122160ee2d..bbe42edad59d 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -922,8 +922,7 @@ struct buffer_head *folio_alloc_buffers(struct folio *folio, unsigned long size,
 	long offset;
 	struct mem_cgroup *memcg, *old_memcg;
 
-	/* The folio lock pins the memcg */
-	memcg = folio_memcg(folio);
+	memcg = get_mem_cgroup_from_folio(folio);
 	old_memcg = set_active_memcg(memcg);
 
 	head = NULL;
@@ -944,6 +943,7 @@ struct buffer_head *folio_alloc_buffers(struct folio *folio, unsigned long size,
 	}
 out:
 	set_active_memcg(old_memcg);
+	mem_cgroup_put(memcg);
 	return head;
 /*
  * In case anything failed, we just free everything we got.