linux-kernel - [PATCH RFC 15/28] mm: page_io: prevent memory cgroup release in page

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Message-Id: <20250415024532.26632-16-songmuchun@bytedance.com>
Date: Tue, 15 Apr 2025 10:45:19 +0800
From: Muchun Song <songmuchun@...edance.com>
To: hannes@...xchg.org,
	mhocko@...nel.org,
	roman.gushchin@...ux.dev,
	shakeel.butt@...ux.dev,
	muchun.song@...ux.dev,
	akpm@...ux-foundation.org,
	david@...morbit.com,
	zhengqi.arch@...edance.com,
	yosry.ahmed@...ux.dev,
	nphamcs@...il.com,
	chengming.zhou@...ux.dev
Cc: linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-mm@...ck.org,
	hamzamahfooz@...ux.microsoft.com,
	apais@...ux.microsoft.com,
	Muchun Song <songmuchun@...edance.com>
Subject: [PATCH RFC 15/28] mm: page_io: prevent memory cgroup release in page_io module

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 swap_writepage() and
bio_associate_blkg_from_page().

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

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/page_io.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index 4bce19df557b..5894e2ff97ef 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -280,10 +280,14 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		folio_unlock(folio);
 		return 0;
 	}
+
+	rcu_read_lock();
 	if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) {
+		rcu_read_unlock();
 		folio_mark_dirty(folio);
 		return AOP_WRITEPAGE_ACTIVATE;
 	}
+	rcu_read_unlock();
 
 	__swap_writepage(folio, wbc);
 	return 0;
@@ -308,11 +312,11 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
 	struct cgroup_subsys_state *css;
 	struct mem_cgroup *memcg;
 
-	memcg = folio_memcg(folio);
-	if (!memcg)
+	if (!folio_memcg_charged(folio))
 		return;
 
 	rcu_read_lock();
+	memcg = folio_memcg(folio);
 	css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys);
 	bio_associate_blkg_from_css(bio, css);
 	rcu_read_unlock();
-- 
2.20.1