Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups
From: Mike Galbraith <efault@gmx.de>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Markus Trippelsdorf <markus@trippelsdorf.de>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <20101116150319.GA3475@redhat.com>
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	 <1289821590.16406.47.camel@maggy.simson.net>
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Date: Tue, 16 Nov 2010 08:41:48 -0700
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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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