linux-kernel - [PATCH v1 08/26] buffer: prevent memory cgroup release in folio_alloc

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Message-ID: <f62ef59c751a710b0e1adff07876c02942664a7b.1761658310.git.zhengqi.arch@bytedance.com>
Date: Tue, 28 Oct 2025 21:58:21 +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@...hat.com,
	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,
	akpm@...ux-foundation.org
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 v1 08/26] buffer: prevent memory cgroup release in folio_alloc_buffers()

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 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.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 fs/buffer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 6a8752f7bbedb..bc93d0b1d0c30 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -925,8 +925,7 @@ 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;
@@ -947,6 +946,7 @@ 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.
-- 
2.20.1