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

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Message-ID: <20131128114542.GA3826@redhat.com>
Date:	Thu, 28 Nov 2013 12:45:42 +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 Wed, Nov 27, 2013 at 01:31:17PM -0500, Tejun Heo wrote:
> > On Wed, Nov 27, 2013 at 10:07:03AM +0800, zhang.yi20@....com.cn wrote:
> > > Userspace process doesn't want the PF_NO_SETAFFINITY, but its parent may be
> > > a kernel worker thread which has PF_NO_SETAFFINITY set, and this worker thread
> > > can do kernel_thread() to create the child.
> > > Clearing this flag in usersapce child to enable its migrating capability.
> > >
> > >
> > > Signed-off-by: Zhang Yi <zhang.yi20@....com.cn>
> >
> > Acked-by: Tejun Heo <tj@...nel.org>
> >
> > cc'ing Ingo and Peter.  Ingo, I think this one doesn't really suit the
> > workqueue tree.  Can you please pick this one up w/ Oleg's ack added
> > and stable cc'd?  The original patch is
> >
> >   http://article.gmane.org/gmane.linux.kernel/1602429/raw
>
> So I don't get the problem; aren't all usermode helper thingies spawned
> by the khelper task, which doesn't have PG_NO_SETAFFINITY set?

It has? khelper is a workqueue thread, this flag is set by create_worker().

And it does kernel_thread() (not kthread_create()) so the child gets this
flag too.

> The Changelog is not explaining anything much -- so no I will not take
> this patch.

Well, perhaps the changelog can be more verbose and clear...

Zhang, I'm afraid you have to send v3 ;)

Oleg.

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