linux-kernel - Re: [PATCH 3/3] pids: Make it possible to clone tasks with given pids

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Date:	Thu, 17 Nov 2011 16:32:00 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...ux.intel.com>,
	Roland McGrath <roland@...k.frob.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	James Bottomley <jbottomley@...allels.com>
Subject: Re: [PATCH 3/3] pids: Make it possible to clone tasks with given
	pids

On 11/17, Pavel Emelyanov wrote:
>
> +static int set_pidmap(struct pid_namespace *pid_ns, int pid)
> +{
> +	int offset;
> +	struct pidmap *map;
> +
> +	/*
> +	 * When creating a new pid namespace we must make its init
> +	 * have pid == 1 in it.
> +	 */
> +	if (pid_ns->child_reaper == NULL)
> +		return 0;

Do we really need this check? please see below...

> +	/*
> +	 * Don't allow to create a task with a pid which has recently
> +	 * belonged to some other (dead already) task. Only init (of
> +	 * a freshly created namespace) and his clones can do this.
> +	 */
> +	if (pid_ns->last_pid != 1)
> +		return -EPERM;

->last_pid == 1. This means that pid_nr == 1 was already created
in this namespace via CLONE_NEWPID, and the child with this pid
must be ->child_reaper, no?

IOW. if copy_process() allocs the first pid in the new pid_ns, it
always sets ->child_reaper.


Cough. I really think 45a68628 should be reverted ;) IMHO it
complicates the understanding of CLONE_NEWPID logic.

Oleg.

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