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

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Message-Id: <20120119.140621.817165404586593441.davem@davemloft.net>
Date:	Thu, 19 Jan 2012 14:06:21 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	equinox@...c24.net
Cc:	hans.schillstrom@...csson.com, netdev@...r.kernel.org,
	ebiederm@...ssion.com
Subject: Re: RFC Hanging clean-up of a namespace

From: David Lamparter <equinox@...c24.net>
Date: Thu, 19 Jan 2012 20:01:14 +0100

> 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.

The assumption is that the address is moving, which might not be true.
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