linux-kernel - Re: [PATCH 06/16] freezer: make exiting tasks properly unfreezable

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Message-ID: <20110823155221.GB25808@redhat.com>
Date:	Tue, 23 Aug 2011 17:52:21 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	rjw@...k.pl, menage@...gle.com, linux-kernel@...r.kernel.org,
	arnd@...db.de
Subject: Re: [PATCH 06/16] freezer: make exiting tasks properly unfreezable

Hi.

Not a comment, but the question. Probably falls into the "read the
whole series" category too.

On 08/19, Tejun Heo wrote:
>
> There's no point in freezing an exiting task.

This is not clear to me. Probably this is fine, I do not know what
the callers of freeze_processes() actually expect.

> @@ -915,6 +913,12 @@ NORET_TYPE void do_exit(long code)
>
>  	ptrace_event(PTRACE_EVENT_EXIT, code);
>
> +	/*
> +	 * With ptrace notification done, there's no point in freezing from
> +	 * here on.  Disallow freezing.
> +	 */
> +	current->flags |= PF_NOFREEZE;

OK, but what PF_NOFREEZE actually means?

Apart from "dont try to freeze" it means "no need to freeze", yes?

IOW, try_to_freeze_tasks() can succeed even if we have a lot of
exitinig task which can make some activity, say, disk i/o. Is this
correct?

Once again, I do not understand the problem-space at all, jus I am
curious.

Thanks,

Oleg.

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