linux-kernel - [PATCH] cgroup: Remove redundant rcu_read_lock() in spin_lock

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Message-ID: <20250815091430.8694-1-lirongqing@baidu.com>
Date: Fri, 15 Aug 2025 17:14:30 +0800
From: lirongqing <lirongqing@...du.com>
To: <tj@...nel.org>, <hannes@...xchg.org>, <mkoutny@...e.com>,
	<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: Li RongQing <lirongqing@...du.com>
Subject: [PATCH] cgroup: Remove redundant rcu_read_lock() in spin_lock_irq() section

From: Li RongQing <lirongqing@...du.com>

Since spin_lock_irq() already disables preemption and task_css_set()
is protected by css_set_lock, the rcu_read_lock() calls are unnecessary
within the critical section. Remove them to simplify the code.

Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 kernel/cgroup/cgroup.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 312c6a8..db9e00a 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2944,14 +2944,12 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
 
 	/* look up all src csets */
 	spin_lock_irq(&css_set_lock);
-	rcu_read_lock();
 	task = leader;
 	do {
 		cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
 		if (!threadgroup)
 			break;
 	} while_each_thread(leader, task);
-	rcu_read_unlock();
 	spin_unlock_irq(&css_set_lock);
 
 	/* prepare dst csets and commit */
-- 
2.9.4