linux-kernel - Re: [PATCH -next v2] cgroup: Update out-of-date comment in cgroup

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Date:   Wed, 24 May 2023 12:23:13 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Xiu Jianfeng <xiujianfeng@...weicloud.com>
Cc:     lizefan.x@...edance.com, hannes@...xchg.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v2] cgroup: Update out-of-date comment in
 cgroup_migrate()

Hello,

I further edited the comment and applied the patch to cgroup/for-6.5

Thanks.

>From 659db0789c2e66c5d6a52d57008e3a7401a3ffff Mon Sep 17 00:00:00 2001
From: Xiu Jianfeng <xiujianfeng@...weicloud.com>
Date: Wed, 24 May 2023 14:54:31 +0800
Subject: [PATCH] cgroup: Update out-of-date comment in cgroup_migrate()

Commit 674b745e22b3 ("cgroup: remove rcu_read_lock()/rcu_read_unlock()
in critical section of spin_lock_irq()") has removed the rcu_read_lock,
which makes the comment out-of-date, so update it.

tj: Updated the comment a bit.

Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/cgroup/cgroup.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 9d809191a54f..f329f49529a2 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2872,9 +2872,9 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
 	struct task_struct *task;
 
 	/*
-	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
-	 * already PF_EXITING could be freed from underneath us unless we
-	 * take an rcu_read_lock.
+	 * The following thread iteration should be inside an RCU critical
+	 * section to prevent tasks from being freed while taking the snapshot.
+	 * spin_lock_irq() implies RCU critical section here.
 	 */
 	spin_lock_irq(&css_set_lock);
 	task = leader;
-- 
2.40.1