linux-kernel - [PATCH 3/8] memcg: mem_cgroup_get_from

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Message-ID: <20251225232116.294540-4-shakeel.butt@linux.dev>
Date: Thu, 25 Dec 2025 15:21:11 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	SeongJae Park <sj@...nel.org>,
	Meta kernel team <kernel-team@...a.com>,
	linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	damon@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/8] memcg: mem_cgroup_get_from_ino() returns NULL on error

Change mem_cgroup_get_from_ino() to return NULL on error instead of
ERR_PTR values. This simplifies the API: NULL indicates failure, and a
valid pointer indicates success with a CSS reference held that the
caller must release via mem_cgroup_put().

Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
---
 mm/memcontrol.c     | 6 ++----
 mm/shrinker_debug.c | 2 +-
 2 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e85816960e38..92beb74482fa 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3624,17 +3624,15 @@ struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
 {
 	struct cgroup *cgrp;
 	struct cgroup_subsys_state *css;
-	struct mem_cgroup *memcg;
+	struct mem_cgroup *memcg = NULL;
 
 	cgrp = cgroup_get_from_id(ino);
 	if (IS_ERR(cgrp))
-		return ERR_CAST(cgrp);
+		return NULL;
 
 	css = cgroup_get_e_css(cgrp, &memory_cgrp_subsys);
 	if (css)
 		memcg = container_of(css, struct mem_cgroup, css);
-	else
-		memcg = ERR_PTR(-ENOENT);
 
 	cgroup_put(cgrp);
 
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index 20eaee3e97f7..8aaeb8f5c3af 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -130,7 +130,7 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
 		memcg = mem_cgroup_get_from_ino(ino);
-		if (!memcg || IS_ERR(memcg))
+		if (!memcg)
 			return -ENOENT;
 
 		if (!mem_cgroup_online(memcg)) {
-- 
2.47.3