netdev - Re: [PATCH] wireless extensions: play with netns

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Date:	Wed, 17 Jun 2009 16:54:12 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Johannes Berg <johannes@...solutions.net>
Cc:	John Linville <linville@...driver.com>,
	Netdev <netdev@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH] wireless extensions: play with netns

Johannes Berg <johannes@...solutions.net> writes:

> On Wed, 2009-06-17 at 16:24 -0700, Eric W. Biederman wrote:
>
>> > So it looks like I can also use rcu_read_lock(), but there's no
>> > for_each_net_rcu(), should there be?
>> 
>> I'm not using rcu safe list manipulation.  What makes it look like
>> rcu_read_lock() is safe?
>
> Indeed. I was looking at rcu_barrier() only. How about the patch below?
>
> johannes
>
> Subject: net: make namespace iteration possible under RCU
>
> We already call rcu_barrier(), so all we need to take
> care of is using proper RCU list add/del primitives.

This of course gives you a network namespace that can be found by for_each_net rcu
while the per net exit functions are running.  I think that opens up to races
that I don't want to think about.

I still haven't tracked down how I am occasionally getting time wait sockets
with an invalid network namespace.

Eric
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