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

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Message-ID: <20111207185343.GA3209@redhat.com>
Date:	Wed, 7 Dec 2011 19:53:43 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
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

Hi Cyrill,

Sorry, I didn't read this patch yet, but

On 12/06, Cyrill Gorcunov wrote:
>
> +static void *children_seq_start(struct seq_file *seq, loff_t *pos)
> +{
> +	struct task_struct *task;
> +
> +	rcu_read_lock();
> +	task = seq->private;
> +	if (task)
> +		return seq_list_start(&task->children, *pos);

This looks "obviously wrong".

We can not trust ->children->next after rcu_read_unlock(). Another
rcu_read_lock() can't help.

Once again, I can be easily wrong, need to read the patch first.

Oleg.

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