linux-kernel - Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

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Date:	Tue, 16 Nov 2010 08:41:48 -0700
From:	Mike Galbraith <efault@....de>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

On Tue, 2010-11-16 at 16:03 +0100, Oleg Nesterov wrote:
> On 11/16, Mike Galbraith wrote:
> >
> > On Tue, 2010-11-16 at 14:04 +0100, Oleg Nesterov wrote:
> > > However, I must admit I dislike this check. Because, looking at this
> > > code, it is not clear why do we check PF_EXITING. It looks as if it
> > > is needed for correctness.
> >
> > Is _not_ needed I presume.
> >
> > I'll remove it, I'm not overly attached (a t t a..;) to it.
> 
> Argh!
> 
> I was wrong, it _is_ needed for correctness. Yes, it is always safe
> to read the pointer, but
> 
> > > Yes, sure, rq->lock should ensure signal->autogroup can't go away.
> > > (even if it can be changed under us). And it does, we are moving all
> > > threads before kref_put().
> >
> > (yeah)
> 
> Exactly. And this means we can _only_ assume it can't go away if
> autogroup_move_group() can see us on ->thread_group list.

Aha!

> Perhaps this deserve a commen (unless I missed something again).
> 
> Mike, sorry for confusion.

Oh no, thank you.  I hadn't figured it out yet, was going to go back and
poke rt kernel with sharp sticks.  (exit can be one scary beast)

	-Mike

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