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

[Oleg Nesterov <oleg@tv-sign.ru>]

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();

?

> It may be a good time to solve this problem now. :-)

Yes, I think so :)

Oleg.

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