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Date: Mon, 16 Jan 2012 20:20:21 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Pavel Emelyanov <xemul@parallels.com>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Tejun Heo <tj@kernel.org>, Andrew Vagin <avagin@openvz.org>,
        Vasiliy Kulikov <segoon@openwall.com>
Subject: Re: [RFC] fs, proc: Introduce /proc/<pid>/task/<tid>/children entry
 v6
Message-ID: <20120116162021.GH2998@moon>
References: <20120116153231.GF2998@moon>
 <20120116161114.GA17727@redhat.com>
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On Mon, Jan 16, 2012 at 05:11:14PM +0100, Oleg Nesterov wrote:
> On 01/16, Cyrill Gorcunov wrote:
> >
> > +get_children_pid(struct proc_pid_children_iter *iter, struct pid *pid_prev, loff_t pos)
> > +{
> > +	struct task_struct *start, *task;
> > +	struct pid *pid = NULL;
> > +
> > +	read_lock(&tasklist_lock);
> > +
> > +	start = pid_task(iter->pid_start, PIDTYPE_PID);
> > +	if (!start)
> > +		goto out;
> > +
> > +	/*
> > +	 * Lets try to continue searching first, this gives
> > +	 * us significant speedup on children-rich processes.
> > +	 */
> > +	if (pid_prev) {
> > +		task = pid_task(pid_prev, PIDTYPE_PID);
> > +		if (task && task->real_parent == start &&
> > +		    !(list_empty(&task->sibling))) {
> 
> Damn. No, this is wrong.
> 
> Damn! Yes, it was we who told you to check list_empty(sibling) ;)
> 
> But this is not enough. exit_ptrace() can do list_move() without
> changing ->real_parent.
> 
> I'll try to think. At first glance we can rely on EXIT_DEAD, but
> I'd like to avoid this, I think EXIT_DEAD should die.
> 

Ouch! Thanks for catching this Oleg. I'll try to come with something
to show as well.

	Cyrill