linux-kernel - Re: [PATCH] fs, proc: Introduce the /proc/<pid>/children entry v2

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Message-ID: <20111209171149.GU21678@moon>
Date:	Fri, 9 Dec 2011 21:11:49 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	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>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Andrew Vagin <avagin@...nvz.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs, proc: Introduce the /proc/<pid>/children entry v2

On Fri, Dec 09, 2011 at 05:55:36PM +0100, Oleg Nesterov wrote:
...
> 
> To simplify, let's talk about children_seq_start() your patch adds.
> Suppose that we make ->children/sibling "rcu-safe" (we replace
> __unhash_process()->list_del_init() with list_del_rcu, and so on).
> 
> Now, children_seq_start() does:
> 
> 	rcu_read_lock();
> 
> 	list_for_each(child, task->children)
> 		...;
> 
> Suppose that this task exits and reparents the child we are looking at.
> Once reparent_leader() moves it into another list, list_for_each()
> can never stop.
> 
> In short. forget_original_parent() changes the _head_ of the list,
> in some sense.
> 

Yeah, I missed this, my bad! Thanks for explanation, Oleg. I'll
post updated version once I finish it.

	Cyrill
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