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

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Message-Id: <200702181314.29214.rjw@sisk.pl>
Date:	Sun, 18 Feb 2007 13:14:28 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Oleg Nesterov <oleg@...sign.ru>
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 Sunday, 18 February 2007 12:31, Oleg Nesterov wrote:
> On 02/18, Rafael J. Wysocki wrote:
> >
> > On Sunday, 18 February 2007 00:47, Oleg Nesterov wrote:
> > > 
> > > However, this means that sys_vfork() makes impossible to freeze processes
> > > until child exits/execs. Not good.
> > 
> > Yes, but this also is the current behavior.
> 
> Yes, yes, I see.
> 
> I forgot to say that we have another problem: coredumping.
> 
> A thread which does do_coredump() send SIGKILL to ->mm users, and sleeps
> on ->mm->core_startup_done. Now it can't be frozen if sub-thread goes to
> refrigerator. I think this could be solved easily if we add a check to
> refrigerator() as you suggested for ->vfork_donw.
> 
> > I think the real solution would be to use an interruptible completion in the
> > vfork code.  It was discussed some time ago and, IIRC, Ingo had an experimental
> > patch that implemented it.  Still, for the suspend this really is not an issue
> > in practice, so it wasn't merged.
> 
> It is not (afaics) so trivial to do rightly, and with this change the parent
> will be seen as TASK_INTERRUPTIBLE even without freezer in progress.
> 
> A very vague idea: what if parent will do
> 
> 	current->flags |= PF_PLEASE_CONSIDER_ME_AS_FROZEN_BUT_SET_TIF_FREEZE
> 	wait_for_completion(&vfork);
> 	try_to_freeze();
> 
> ?

This should work, but we'll need a separate process flag for it.  If that's
acceptable, I'd call it PF_VFORK_PARENT

Greetings,
Rafael
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