linux-kernel - Re: [PATCH v4] PM / Freezer: Skip zombie/dead processes to reduce freeze latency

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Message-ID: <20250717013158.GF16401@redhat.com>
Date: Thu, 17 Jul 2025 03:31:59 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Zihuan Zhang <zhangzihuan@...inos.cn>
Cc: "rafael J . wysocki" <rafael@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	len brown <len.brown@...el.com>, pavel machek <pavel@...nel.org>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] PM / Freezer: Skip zombie/dead processes to reduce
 freeze latency

Hi Zihuan,

On 07/17, Zihuan Zhang wrote:
>
> >>+			 */
> >>+			if (p == current || p->exit_state || !freeze_task(p))
> >>  				continue;
> >I leave this to you and Rafael, but this change doesn't look safe to me.
> >What if the exiting task does some IO after exit_notify() ?
>
> Tasks that have passed exit_notify() and entered EXIT_ZOMBIE are no longer
> schedulable,

How so? please look at do_exit(). The exiting task is still running
until it does its last __schedule() in do_task_dead().

> so they cannot do I/O anymore. Skipping them during freezing
> should be safe

Oleg.