linux-kernel - Re: [RFC] fs, proc: Introduce /proc/<pid>/task/<tid>/children entry v6

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Message-ID: <20120118182344.GD2889@moon>
Date:	Wed, 18 Jan 2012 22:23:44 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>, Andrew Vagin <avagin@...nvz.org>,
	Vasiliy Kulikov <segoon@...nwall.com>
Subject: Re: [RFC] fs, proc: Introduce /proc/<pid>/task/<tid>/children entry
 v6

On Wed, Jan 18, 2012 at 03:36:31PM +0100, Oleg Nesterov wrote:
> On 01/18, Cyrill Gorcunov wrote:
> >
> > So Oleg, I think you meant something like below? Comment is moved down an
> > list_empty over siblings remans, right?
> 
> Yes, except the comment still looks misleading to me.
> 
> Otherwise looks correct, but I'll try to re-check once again with
> the fresh head. Although I think you should remove me from CC: after
> I found the nonexistent bug ;)
> 

There is no way back from CC ;)

> This is minor, but "freshly created" looks very confusing to me.
> What does it mean? We hold tasklist, we can't race with fork().
> 

Hmm. Sure we keep a lock here, but changes might happen between reads
If only I'm not missing something again.

Look which scenario I've had in mind. We have a task A and children B,C,D,E.
... Here my scenario ended and I realised that you're right. I'll update
the comment.

> Yes we can miss a child, but this has nothing to do with "freshly".
> Just suppose that the parent sleeps, but N children exit after we
> printed their tids. Now the slow paths skips N extra children, we
> miss N tasks.
> 
> Oleg.
> 

	Cyrill
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