linux-kernel - Re: [PATCH next] sched,freezer: prevent tasks from escaping being frozen

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Message-ID: <20250704075718.GA2001818@noisy.programming.kicks-ass.net>
Date: Fri, 4 Jul 2025 09:57:18 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: Michal Koutn?? <mkoutny@...e.com>, rafael@...nel.org, pavel@...nel.org,
	timvp@...gle.com, tj@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, lujialin4@...wei.com,
	chenridong@...wei.com
Subject: Re: [PATCH next] sched,freezer: prevent tasks from escaping being
 frozen

On Fri, Jul 04, 2025 at 11:11:52AM +0800, Chen Ridong wrote:

Your patches are mangled; please educate your MUA.

> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -71,19 +71,20 @@ bool __refrigerator(bool check_kthr_stop)
>         for (;;) {
>                 bool freeze;
> 
> -               raw_spin_lock_irq(&current->pi_lock);
> -               WRITE_ONCE(current->__state, TASK_FROZEN);
> -               /* unstale saved_state so that __thaw_task() will wake
> us up */
> -               current->saved_state = TASK_RUNNING;
> -               raw_spin_unlock_irq(&current->pi_lock);
> -
>                 spin_lock_irq(&freezer_lock);
> -               freeze = freezing(current) && !(check_kthr_stop &&
> kthread_should_stop());
> +               freeze = (freezing(current) || !cgroup_thawed(current))
> +                        && !(check_kthr_stop && kthread_should_stop());

This makes no sense to me; why can't this stay in cgroup_freezing()?

Also, can someone please fix that broken comment style there.

>                 spin_unlock_irq(&freezer_lock);
> 
>                 if (!freeze)
>                         break;
> 
> +               raw_spin_lock_irq(&current->pi_lock);
> +               WRITE_ONCE(current->__state, TASK_FROZEN);
> +               /* unstale saved_state so that __thaw_task() will wake
> us up */
> +               current->saved_state = TASK_RUNNING;
> +               raw_spin_unlock_irq(&current->pi_lock);
> +

And I'm not quite sure I understand this hunk either. If we bail out,
current->__state is reset to TASK_RUNNING, so what's the problem?