From: Muchun Song <songmuchun@bytedance.com>
Date: Thu, 5 Mar 2026 11:52:33 +0000 (+0800)
Subject: mm: memcontrol: prevent memory cgroup release in mem_cgroup_swap_full()
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=c863aded26d1f98247af2719b1e3ed01e3d0d4f6;p=thirdparty%2Fkernel%2Flinux.git

mm: memcontrol: prevent memory cgroup release in mem_cgroup_swap_full()

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 mem_cgroup_swap_full().

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

Link: https://lore.kernel.org/21d1abab7342615745ea4c18a88237335ab44d13.1772711148.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>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d7d4b44c5af5..10021cef176b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5338,27 +5338,29 @@ long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg)
 bool mem_cgroup_swap_full(struct folio *folio)
 {
 	struct mem_cgroup *memcg;
+	bool ret = false;
 
 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
 	if (vm_swap_full())
 		return true;
-	if (do_memsw_account())
-		return false;
+	if (do_memsw_account() || !folio_memcg_charged(folio))
+		return ret;
 
+	rcu_read_lock();
 	memcg = folio_memcg(folio);
-	if (!memcg)
-		return false;
-
 	for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) {
 		unsigned long usage = page_counter_read(&memcg->swap);
 
 		if (usage * 2 >= READ_ONCE(memcg->swap.high) ||
-		    usage * 2 >= READ_ONCE(memcg->swap.max))
-			return true;
+		    usage * 2 >= READ_ONCE(memcg->swap.max)) {
+			ret = true;
+			break;
+		}
 	}
+	rcu_read_unlock();
 
-	return false;
+	return ret;
 }
 
 static int __init setup_swap_account(char *s)