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Date: Fri, 21 Dec 2012 16:31:52 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Linux Containers <containers@lists.linux-foundation.org>,
        linux-kernel@vger.kernel.org, Serge Hallyn <serge@hallyn.com>,
        Gao feng <gaofeng@cn.fujitsu.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 07/11] pidns: Wait in zap_pid_ns_processes until
	pid_ns->nr_hashed == 1
Message-ID: <20121221153152.GA17250@redhat.com>
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On 12/21, Oleg Nesterov wrote:
>
> Once again, the parent namespace injects the task T after ns->reaper
> sees nr_hashed == 1 and returns. Suppose that reaper's parent does
> do_wait() and free_pidmap() clears the bit == 1.
>
> Now, what if T doesn't exit but forks? We must not re-create the
> task with pid_nr == 1 in the dead namespace. Normally this can't
> happen, RESERVED_PIDS logic in alloc_pidmap() saves us. But it
> seems that we need
>
> 	- .extra1 = &zero,
> 	+ .extra1 = &one,
>
> in pid_ns_ctl_table.

Oh, and another problem, or I am totally confused.

T forks and creates the child C1. C1 creates C2. What if C1 exits?
It will try to reparent C2 to the dead/freed ns->child_reaper.

In short. We shouldn't allow alloc_pid() if ns->child_reaper is dying,
I think. nr_hashed == -1 doesn't really work.

Oleg.