linux-kernel - [PATCH v1 07/26] mm: memcontrol: prevent memory cgroup release in get_mem_cgroup_from

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Message-ID: <9eca65dec044d4352bee84511fb58960a1402ddf.1761658310.git.zhengqi.arch@bytedance.com>
Date: Tue, 28 Oct 2025 21:58:20 +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 07/26] mm: memcontrol: prevent memory cgroup release in get_mem_cgroup_from_folio()

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 get_mem_cgroup_from_folio().

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>
---
 mm/memcontrol.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d484b632c790f..1da3ad77054d3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -973,14 +973,19 @@ struct mem_cgroup *get_mem_cgroup_from_current(void)
  */
 struct mem_cgroup *get_mem_cgroup_from_folio(struct folio *folio)
 {
-	struct mem_cgroup *memcg = folio_memcg(folio);
+	struct mem_cgroup *memcg;
 
 	if (mem_cgroup_disabled())
 		return NULL;
 
+	if (!folio_memcg_charged(folio))
+		return root_mem_cgroup;
+
 	rcu_read_lock();
-	if (!memcg || WARN_ON_ONCE(!css_tryget(&memcg->css)))
-		memcg = root_mem_cgroup;
+retry:
+	memcg = folio_memcg(folio);
+	if (unlikely(!css_tryget(&memcg->css)))
+		goto retry;
 	rcu_read_unlock();
 	return memcg;
 }
-- 
2.20.1