linux-kernel - [PATCH v1 19/26] mm: swap: prevent lruvec release in swap module

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Message-ID: <c8b190b1b4f2690f12dee0e334e4c0b3f94ad260.1761658311.git.zhengqi.arch@bytedance.com>
Date: Tue, 28 Oct 2025 21:58:32 +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 19/26] mm: swap: prevent lruvec release in swap module

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 lru_note_cost_refault() and
lru_activate().

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/swap.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index ec0c654e128dc..0606795f3ccf3 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -412,18 +412,20 @@ static void lru_gen_inc_refs(struct folio *folio)
 
 static bool lru_gen_clear_refs(struct folio *folio)
 {
-	struct lru_gen_folio *lrugen;
 	int gen = folio_lru_gen(folio);
 	int type = folio_is_file_lru(folio);
+	unsigned long seq;
 
 	if (gen < 0)
 		return true;
 
 	set_mask_bits(&folio->flags.f, LRU_REFS_FLAGS | BIT(PG_workingset), 0);
 
-	lrugen = &folio_lruvec(folio)->lrugen;
+	rcu_read_lock();
+	seq = READ_ONCE(folio_lruvec(folio)->lrugen.min_seq[type]);
+	rcu_read_unlock();
 	/* whether can do without shuffling under the LRU lock */
-	return gen == lru_gen_from_seq(READ_ONCE(lrugen->min_seq[type]));
+	return gen == lru_gen_from_seq(seq);
 }
 
 #else /* !CONFIG_LRU_GEN */
-- 
2.20.1