linux-kernel - [PATCH v1 18/26] mm: zswap: prevent lruvec release in zswap_folio

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Message-ID: <c85c86746a3103bac3657934a2655c1eb81ff290.1761658311.git.zhengqi.arch@bytedance.com>
Date: Tue, 28 Oct 2025 21:58:31 +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>,
	Nhat Pham <nphamcs@...il.com>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v1 18/26] mm: zswap: prevent lruvec release in zswap_folio_swapin()

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

In the near future, a folio will no longer pin its corresponding
memory cgroup. So an lruvec returned by folio_lruvec() could be
released without the rcu read lock or a reference to its memory
cgroup.

In the current patch, the rcu read lock is employed to safeguard
against the release of the lruvec in zswap_folio_swapin().

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

Signed-off-by: Muchun Song <songmuchun@...edance.com>
Acked-by: Nhat Pham <nphamcs@...il.com>
Reviewed-by: Chengming Zhou <chengming.zhou@...ux.dev>
Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 mm/zswap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/zswap.c b/mm/zswap.c
index 5d0f8b13a958d..a341814468b95 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -664,8 +664,10 @@ void zswap_folio_swapin(struct folio *folio)
 	struct lruvec *lruvec;
 
 	if (folio) {
+		rcu_read_lock();
 		lruvec = folio_lruvec(folio);
 		atomic_long_inc(&lruvec->zswap_lruvec_state.nr_disk_swapins);
+		rcu_read_unlock();
 	}
 }
 
-- 
2.20.1