[PATCH 08/11] pidns: Deny strange cases when creating pid namespaces.

[Gao feng]

on 2012/11/17 00:35, Eric W. Biederman wrote:
> From: "Eric W. Biederman" <ebiederm at xmission.com>
> 
> task_active_pid_ns(current) != current->ns_proxy->pid_ns will
> soon be allowed to support unshare and setns.
> 
> The definition of creating a child pid namespace when
> task_active_pid_ns(current) != current->ns_proxy->pid_ns could be that
> we create a child pid namespace of current->ns_proxy->pid_ns.  However
> that leads to strange cases like trying to have a single process be
> init in multiple pid namespaces, which is racy and hard to think
> about.
> 
> The definition of creating a child pid namespace when
> task_active_pid_ns(current) != current->ns_proxy->pid_ns could be that
> we create a child pid namespace of task_active_pid_ns(current).  While
> that seems less racy it does not provide any utility.
> 
> Therefore define the semantics of creating a child pid namespace when
> task_active_pid_ns(current) != current->ns_proxy->pid_ns to be that the
> pid namespace creation fails.  That is easy to implement and easy
> to think about.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
> ---

Acked-by: Gao feng <gaofeng at cn.fujitsu.com>