linux-kernel - Re: [PATCH 1/2] pidns: guarantee that the pidns init will be the last pidns process reaped

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Date:	Thu, 31 May 2012 14:32:51 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Louis Rilling <louis.rilling@...labs.com>,
	Mike Galbraith <efault@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] pidns: guarantee that the pidns init will be the
 last pidns process reaped

On 05/30/2012 10:15 PM, Oleg Nesterov wrote:
> From: Eric W. Biederman <ebiederm@...ssion.com>
> 
> Today we have a two-fold bug.  Sometimes release_task on pid == 1 in a
> pid namespace can run before other processes in a pid namespace have had
> release task called.  With the result that pid_ns_release_proc can be
> called before the last proc_flus_task() is done using
> upid->ns->proc_mnt, resulting in the use of a stale pointer.  This same
> set of circumstances can lead to waitpid(...) returning for a processes
> started with clone(CLONE_NEWPID) before the every process in the pid
> namespace has actually exited.
> 
> To fix this modify zap_pid_ns_processess wait until all other processes
> in the pid namespace have exited, even EXIT_DEAD zombies.
> 
> The delay_group_leader and related tests ensure that the thread gruop
> leader will be the last thread of a process group to be reaped, or to
> become EXIT_DEAD and self reap.  With the change to zap_pid_ns_processes
> we get the guarantee that pid == 1 in a pid namespace will be the last
> task that release_task is called on.
> 
> With pid == 1 being the last task to pass through release_task
> pid_ns_release_proc can no longer be called too early nor can wait
> return before all of the EXIT_DEAD tasks in a pid namespace have exited.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: Pavel Emelyanov <xemul@...allels.com>

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