netdev - Re: RFC Hanging clean-up of a namespace

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Date:	Thu, 19 Jan 2012 20:01:14 +0100
From:	David Lamparter <equinox@...c24.net>
To:	David Miller <davem@...emloft.net>
Cc:	hans.schillstrom@...csson.com, netdev@...r.kernel.org,
	ebiederm@...ssion.com
Subject: Re: RFC Hanging clean-up of a namespace

On Thu, Jan 19, 2012 at 12:40:02PM -0500, David Miller wrote:
> From: Hans Schillstrom <hans.schillstrom@...csson.com>
> Date: Thu, 19 Jan 2012 12:07:09 +0100
> 
> > Closing of a namespace (container) can be delayed by ~ 2 minutes 
> > due to tcp timers ex tcp time wait (and of cource other things too).
> > 
> > I think there should be some kind of "forced close" of the Network stack
> > in ex free_nsproxy() 
> 
> I think this is unwise.
> 
> Keeping the timewait sockets around is necessary to absorb any lingering
> packets in the network meant for those sockets.
> 
> If you truncate this activity, and then try to create another socket with
> the same ID you'll run into the very problems time-wait is meant to
> solve.

A network namespace is for practical matters a separate host on the
network. Killing the namespace therefore is akin to shutting down that
host, which on a real metal host doesn't wait for timewait sockets
either.

Creating a socket with the same parameters would actually require
installing a network environment similar to the closed namespace first;
if an user really does that he can reasonably anticipate the same issues
as arise from removing a host from the network and giving its address to
another host.

-David
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