linux-kernel - [PATCH 3/3] cgroup: Remove unused cgroup_subsys::post

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Message-Id: <20250904074505.1722678-4-zhouchuyi@bytedance.com>
Date: Thu,  4 Sep 2025 15:45:05 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: tj@...nel.org,
	mkoutny@...e.com,
	hannes@...xchg.org,
	longman@...hat.com
Cc: linux-kernel@...r.kernel.org,
	Chuyi Zhou <zhouchuyi@...edance.com>
Subject: [PATCH 3/3] cgroup: Remove unused cgroup_subsys::post_attach

cgroup_subsys::post_attach callback was introduced in commit 5cf1cacb49ae
("cgroup, cpuset: replace cpuset_post_attach_flush() with
cgroup_subsys->post_attach callback") and only cpuset would use this
callback to wait for the mm migration to complete at the end of
__cgroup_procs_write(). Since the previous patch defer the flush operation
until returning to userspace, no one use this callback now. Remove this
callback from cgroup_subsys.

Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
---
 include/linux/cgroup-defs.h | 1 -
 kernel/cgroup/cgroup.c      | 4 ----
 2 files changed, 5 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 6b93a64115fe9..432abdfdb2593 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -746,7 +746,6 @@ struct cgroup_subsys {
 	int (*can_attach)(struct cgroup_taskset *tset);
 	void (*cancel_attach)(struct cgroup_taskset *tset);
 	void (*attach)(struct cgroup_taskset *tset);
-	void (*post_attach)(void);
 	int (*can_fork)(struct task_struct *task,
 			struct css_set *cset);
 	void (*cancel_fork)(struct task_struct *task, struct css_set *cset);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 312c6a8b55bb7..75819bb2f1148 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -3033,10 +3033,6 @@ void cgroup_procs_write_finish(struct task_struct *task, bool threadgroup_locked
 	put_task_struct(task);
 
 	cgroup_attach_unlock(threadgroup_locked);
-
-	for_each_subsys(ss, ssid)
-		if (ss->post_attach)
-			ss->post_attach();
 }
 
 static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
-- 
2.20.1