linux-kernel - Re: [PATCH v3 1/1] PM / Freezer: Skip zombie/dead processes to

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Message-ID: <20250716161624.GD16401@redhat.com>
Date: Wed, 16 Jul 2025 18:16:24 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Zihuan Zhang <zhangzihuan@...inos.cn>,
	"Rafael J. Wysocki" <rafael@...nel.org>, pavel@...nel.org,
	len.brown@...el.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] PM / Freezer: Skip zombie/dead processes to

I don't like the patch Zihuan, but

On 07/07, Peter Zijlstra wrote:
>
> Anyway, this seems to suggest something relatively simple like this here
> should do:
>
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index 8d530d0949ff..8b7cecd17564 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -162,20 +162,22 @@ static bool __freeze_task(struct task_struct *p)
>   */
>  bool freeze_task(struct task_struct *p)
>  {
> -	unsigned long flags;
> -
> -	spin_lock_irqsave(&freezer_lock, flags);
> -	if (!freezing(p) || frozen(p) || __freeze_task(p)) {
> -		spin_unlock_irqrestore(&freezer_lock, flags);
> +	/*
> +	 * User tasks get NOFREEZE in do_task_dead().
> +	 */
> +	if ((p->flags & (PF_NOFREEZE | PF_KTHREAD)) == PF_NOFREEZE)
>  		return false;
> -	}

I don't understand your change...

It probably makes sense to avoid freezer_lock when PF_NOFREEZE is set but
it can't change the current behaciour, freezing() -> freezing_slow_path()
checks PF_NOFREEZE too and returns false in this case.

Oleg.