linux-kernel - Re: [PATCH 0/1][V3] Handle reboot in a child pid namespace

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Message-ID: <4EDBFD67.1040009@free.fr>
Date:	Mon, 05 Dec 2011 00:08:23 +0100
From:	Daniel Lezcano <daniel.lezcano@...e.fr>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
CC:	akpm@...ux-foundation.org, serge.hallyn@...onical.com,
	oleg@...hat.com, containers@...ts.linux-foundation.org,
	gkurz@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/1][V3] Handle reboot in a child pid namespace

On 12/04/2011 10:27 PM, Henrique de Moraes Holschuh wrote:
> On Sun, 04 Dec 2011, Daniel Lezcano wrote:
>>  * V3
>>    - removed lock and serialization of pid_ns_reboot
>>  * V2
>>    - added a lock for the pid namespace to prevent racy call
>>      to the 'reboot' syscall
>>    - Moved 'reboot' command assigned in zap_pid_ns_processes
>>      instead of wait_task_zombie
>>    - added tasklist lock around force_sig
>>    - added do_exit in pid_ns_reboot
>>    - used task_active_pid_ns instead of declaring a new variable in sys_reboot
>>    - moved code up before POWER_OFF changed to HALT in sys_reboot
> Daniel, can you address Miquel's concern?  Is it a valid concern, or
> not?  I assume CAP_REBOOT functionality is still in place inside the
> container, so it really does look like userspace would need to know
> whether it should drop CAP_REBOOT or not, in order to automatically use
> the new feature.

Hmm, I missed its email. I think it is worth to have such ability to
detect how behaves the reboot syscall vs the pid ns. At present, if we
call 'reboot' in a child pid namespace, that will affect the host, we
are changing this behavior with this patch. I don't think there is any
application doing a shutdown from a child pid namespace, that don't
makes sense as the shutdown is invoked after killing all the processes
on the system and that could only be done from the init_pid_ns.

I would like to address this in a separate patch in order to discuss the
best way to do that. Adding a fake 'reboot' parameter returning EINVAL
or 0 seems a good solution to detect at runtime if the shutdown is
correctly supported inside a container.

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