[PATCH -next] cgroup: Remove out-of-date comment in cgroup_migrate()

[PATCH -next] cgroup: Remove out-of-date comment in cgroup_migrate()

[Xiu Jianfeng]

From: Xiu Jianfeng <xiujianfeng@huawei.com>

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which makes the comment out-of-date, so remove it.

Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
---
 kernel/cgroup/cgroup.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index d8ba2c67910d..415d51c713ad 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2871,11 +2871,6 @@ 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.
-	 */
 	spin_lock_irq(&css_set_lock);
 	task = leader;
 	do {
-- 
2.17.1

Re: [PATCH -next] cgroup: Remove out-of-date comment in cgroup_migrate()

[Tejun Heo]

On Tue, May 23, 2023 at 07:14:56PM +0800, Xiu Jianfeng wrote:
> From: Xiu Jianfeng <xiujianfeng@huawei.com>
> 
> 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 which makes the comment out-of-date, so remove it.
> 
> Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>

So, that removed rcu_read_lock() because it's implied by the irq disable but
the comment content is still useful in describing what's preventing
use-after-free. Can you please update the comment accordingly instead?

Thanks.

-- 
tejun

Re: [PATCH -next] cgroup: Remove out-of-date comment in cgroup_migrate()

[Xiu Jianfeng]

On 2023/5/24 3:09, Tejun Heo wrote:
> On Tue, May 23, 2023 at 07:14:56PM +0800, Xiu Jianfeng wrote:
>> From: Xiu Jianfeng <xiujianfeng@huawei.com>
>>
>> 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 which makes the comment out-of-date, so remove it.
>>
>> Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
> 
> So, that removed rcu_read_lock() because it's implied by the irq disable but
> the comment content is still useful in describing what's preventing
> use-after-free. Can you please update the comment accordingly instead?

sure, I would send a v2.

> 
> Thanks.
>