linux-kernel - Re: [RFC][PATCH 0/3] fork: Add the ability to create tasks with?given pids

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Date:	Sun, 27 Nov 2011 17:24:56 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pedro Alves <pedro@...esourcery.com>
Cc:	Pavel Emelyanov <xemul@...allels.com>, Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	James Bottomley <jbottomley@...allels.com>
Subject: Re: [RFC][PATCH 0/3] fork: Add the ability to create tasks
	with?given pids

On 11/25, Pedro Alves wrote:
>
> From the perspective of a client that is
> going to use this on a live system, CLONE_CHILD_USEPIDS seems a little better,
> in that the pid race is only against another task reusing the same pid,

Yes. Except you can't use on a live system at all. It simply doesn't
work after the first "normal" clone() without CLONE_CHILD_USEPIDS.

Although we can probably allow CLONE_CHILD_USEPIDS for CAP_SYS_ADMIN.

> while with setting last_pid, you have a try/whoops-not-the-pid-I-want/kill/retry/rinse/repeat/
> loop racing against all fork/clone's in the system,

Yes, setting last_pid can race with another fork(). I agree this
sucks. But simple ;)

Oleg.

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