From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751228AbdAWMHz (ORCPT <rfc822;w@1wt.eu>);
        Mon, 23 Jan 2017 07:07:55 -0500
Received: from mx1.redhat.com ([209.132.183.28]:56320 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751196AbdAWMHo (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 23 Jan 2017 07:07:44 -0500
Date: Mon, 23 Jan 2017 13:07:35 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        John Stultz <john.stultz@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Michal Hocko <mhocko@suse.com>,
        Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>,
        Mateusz Guzik <mguzik@redhat.com>, linux-kernel@vger.kernel.org,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Konstantin Khorenko <khorenko@virtuozzo.com>
Subject: Re: [PATCH] introduce the walk_process_tree() helper
Message-ID: <20170123120735.GC11827@redhat.com>
References: <20170119164346.4214-1-ptikhomirov@virtuozzo.com>
 <20170123115715.GB11827@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170123115715.GB11827@redhat.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 23 Jan 2017 12:07:39 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 01/23, Oleg Nesterov wrote:
>
> Add the new helper to walk the process tree, the next patch adds a user.
> Note that it visits the group leaders only, proc_visitor can do
> for_each_thread itself or we can trivially extend walk_process_tree() to
> do this.

Please consider this patch as a preparation for your change, or feel free
to fold this code into your patch.

Now you can simply do

	int xxx(struct task_struct *p, void *data)
	{
		if (p->signal->has_child_subreaper ||
		    is_child_reaper(task_pid(p))
			return 0;
		p->signal->has_child_subreaper = 1;
		return 1;
	}

	walk_process_tree(xxx, NULL);

walk_process_tree() handles the sub-threads correctly, but "p" is always the
leader so is_child_reaper() is fine, but probably we need a new helper anyway.

Oleg.