linux-kernel - [PATCH v1 01/26] mm: memcontrol: remove dead code of checking parent memory cgroup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <b13ff669bc3f52922e97fa0cc99e54df05585810.1761658310.git.zhengqi.arch@bytedance.com>
Date: Tue, 28 Oct 2025 21:58:14 +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 01/26] mm: memcontrol: remove dead code of checking parent memory cgroup

From: Muchun Song <songmuchun@...edance.com>

Since the no-hierarchy mode has been deprecated after the commit:

  commit bef8620cd8e0 ("mm: memcg: deprecate the non-hierarchical mode").

As a result, parent_mem_cgroup() will not return NULL except when passing
the root memcg, and the root memcg cannot be offline. Hence, it's safe to
remove the check on the returned value of parent_mem_cgroup(). Remove the
corresponding dead code.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 mm/memcontrol.c | 5 -----
 mm/shrinker.c   | 6 +-----
 2 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 93f7c76f0ce96..d5257465c9d75 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3339,9 +3339,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
 		return;
 
 	parent = parent_mem_cgroup(memcg);
-	if (!parent)
-		parent = root_mem_cgroup;
-
 	memcg_reparent_list_lrus(memcg, parent);
 
 	/*
@@ -3632,8 +3629,6 @@ struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
 			break;
 		}
 		memcg = parent_mem_cgroup(memcg);
-		if (!memcg)
-			memcg = root_mem_cgroup;
 	}
 	return memcg;
 }
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 4a93fd433689a..e8e092a2f7f41 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -286,14 +286,10 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 {
 	int nid, index, offset;
 	long nr;
-	struct mem_cgroup *parent;
+	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
 	struct shrinker_info *child_info, *parent_info;
 	struct shrinker_info_unit *child_unit, *parent_unit;
 
-	parent = parent_mem_cgroup(memcg);
-	if (!parent)
-		parent = root_mem_cgroup;
-
 	/* Prevent from concurrent shrinker_info expand */
 	mutex_lock(&shrinker_mutex);
 	for_each_node(nid) {
-- 
2.20.1