Commit 1f6f80c2 authored Mar 05, 2026 by Muchun Song Committed by Andrew Morton Apr 18, 2026

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_writeout() and
bio_associate_blkg_from_page().

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

Link: https://lore.kernel.org/7c3708358412fb02c482d0985feb5e9513a863ef.1772711148.git.zhengqi.arch@bytedance.com


Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Allen Pais <apais@linux.microsoft.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chen Ridong <chenridong@huawei.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Imran Khan <imran.f.khan@oracle.com>
Cc: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yosry Ahmed <yosry@kernel.org>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent f995da53

mm/page_io.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -276,10 +276,14 @@ int swap_writeout(struct folio folio, struct swap_iocb *swap_plug)
		count_mthp_stat(folio_order(folio), MTHP_STAT_ZSWPOUT);
		goto out_unlock;
		}

		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, swap_plug);
		return 0;
		@@ -307,11 +311,11 @@ 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();