linux-kernel - Re: [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug

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Message-ID: <20070217234728.GA679@tv-sign.ru>
Date:	Sun, 18 Feb 2007 02:47:28 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ego@...ibm.com, akpm@...l.org, paulmck@...ibm.com, mingo@...e.hu,
	vatsa@...ibm.com, dipankar@...ibm.com,
	venkatesh.pallipadi@...el.com, linux-kernel@...r.kernel.org,
	Pavel Machek <pavel@....cz>
Subject: Re: [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug

On 02/18, Oleg Nesterov wrote:
>
> On 02/17, Rafael J. Wysocki wrote:
> >
> > Alternatively, we can move the check into refrigerator(), like this:
> > 
> > --- linux-2.6.20-git13.orig/kernel/power/process.c
> > +++ linux-2.6.20-git13/kernel/power/process.c
> > @@ -39,6 +39,11 @@ void refrigerator(void)
> >  	/* Hmm, should we be allowed to suspend when there are realtime
> >  	   processes around? */
> >  	long save;
> > +
> > +	/* Freeze the task unless there is a vfork completion pending */
> > +	if (current->vfork_done)
> > +		return;
> > +
> 
> This means that "current" returns to user space (get_signal_to_deliver
> will clear TIF_SIGPENDING) and runs. While try_to_freeze_tasks() thinks
> it is frozen.

Ah, sorry. I am wrong, current has no PF_FROZEN yet.

However, this means that sys_vfork() makes impossible to freeze processes
until child exits/execs. Not good.

Oleg.

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