linux-kernel - Re: [PATCH] introduce the walk_process

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Message-ID: <20170123120735.GC11827@redhat.com>
Date:   Mon, 23 Jan 2017 13:07:35 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Michal Hocko <mhocko@...e.com>,
        Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        linux-kernel@...r.kernel.org,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Konstantin Khorenko <khorenko@...tuozzo.com>
Subject: Re: [PATCH] introduce the walk_process_tree() helper

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.