linux-kernel - Re: [PATCH]: exec: avoid propagating PF_NO

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Message-ID: <20131128153443.GB11956@redhat.com>
Date:	Thu, 28 Nov 2013 16:34:43 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tejun Heo <htejun@...il.com>, zhang.yi20@....com.cn,
	lkml <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH]: exec: avoid propagating PF_NO_SETAFFINITY into
	userspace child

On 11/28, Peter Zijlstra wrote:
>
> On Thu, Nov 28, 2013 at 09:13:29AM -0500, Tejun Heo wrote:
> > > A single parent process for all usermode helpers makes so much sense;
> > > not doing it is just weird.
> >
> > If we're gonna allow userland to play with the parent attributes,
> > yeah, that'd make sense.  I'm not sure whether that's an interface
> > that we'd want to commit to tho?  Do we really want to tell userland
> > "there will always be a kernel task khelper and if you change that
> > one's attributes all processes forked from it will inherit those
> > attributes no matter what they are."  I think we'd want something more
> > specific cause that's a lot of commitment to things that we haven't
> > carefully thought about.
>
> It seems like a perfectly fine interface to me. And much preferable to
> creating yet another weird interface to manage tasks.

OK. I am not sure, but perhaps this makes sense.

(Although this means that we will always have the problem with the
 recursive UMH_WAIT_* requests).

In this case khelper should be turned into kthread_worker, this looks
simple.

But note that in the longer term we might want even more. We probably
want a non-daemonized thread controlled by the user-space. And even
more, this thread should be per-namespace (this needs a lot more
discussion).

But whataver we do later, I believe that the patch from Zhang should
be applied now.

Oleg.

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