linux-kernel - [PATCH v4 18/31] mm: zswap: prevent memory cgroup release in zswap

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Message-ID: <2dbc70b6cb57d32ae5c888b5623329aecec8414c.1770279888.git.zhengqi.arch@bytedance.com>
Date: Thu,  5 Feb 2026 17:01:37 +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@...nel.org,
	lorenzo.stoakes@...cle.com,
	ziy@...dia.com,
	harry.yoo@...cle.com,
	yosry.ahmed@...ux.dev,
	imran.f.khan@...cle.com,
	kamalesh.babulal@...cle.com,
	axelrasmussen@...gle.com,
	yuanchu@...gle.com,
	weixugc@...gle.com,
	chenridong@...weicloud.com,
	mkoutny@...e.com,
	akpm@...ux-foundation.org,
	hamzamahfooz@...ux.microsoft.com,
	apais@...ux.microsoft.com,
	lance.yang@...ux.dev,
	bhe@...hat.com
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v4 18/31] mm: zswap: prevent memory cgroup release in zswap_compress()

From: Qi Zheng <zhengqi.arch@...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 zswap_compress().

Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>
Acked-by: Muchun Song <muchun.song@...ux.dev>
Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
---
 mm/zswap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/zswap.c b/mm/zswap.c
index 3d2d59ac3f9c2..a9319ecd92b4b 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -893,11 +893,14 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
 	 * to the active LRU list in the case.
 	 */
 	if (comp_ret || !dlen || dlen >= PAGE_SIZE) {
+		rcu_read_lock();
 		if (!mem_cgroup_zswap_writeback_enabled(
 					folio_memcg(page_folio(page)))) {
+			rcu_read_unlock();
 			comp_ret = comp_ret ? comp_ret : -EINVAL;
 			goto unlock;
 		}
+		rcu_read_unlock();
 		comp_ret = 0;
 		dlen = PAGE_SIZE;
 		dst = kmap_local_page(page);
-- 
2.20.1