netdev - Re: [PATCH] netfilter: per netns nf_conntrack

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Message-Id: <1265226227.2861.302.camel@tonnant>
Date:	Wed, 03 Feb 2010 14:43:47 -0500
From:	Jon Masters <jonathan@...masters.org>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Patrick McHardy <kaber@...sh.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] netfilter: per netns nf_conntrack_cachep

On Wed, 2010-02-03 at 21:09 +0200, Alexey Dobriyan wrote:
> On Wed, Feb 03, 2010 at 01:38:09PM -0500, Jon Masters wrote:
> > *). Per namespace cacheing allocation (the cachep bits). We know it's
> > still possible for weirdness to happen in the SLAB cache here.
> 
> Tiny race, needs reproducer.

Maybe. I think it's worth fixing anyway.

> > *). Per namespace hashsize tracking. Existing code corrupts hashtables
> > if the global size is changed when there is more than one netns
> 
> I think, no.
> Changing hash size will change hashsize for all netns, current and future.

Nope. Look at the logic in nf_conntrack_set_hashsize where you iterate
over init_net.ct.hash but don't touch other namespaces. So then you go
setting nf_conntrack_htable_size and will deference that in accessing
other per-namespace hashtables using the wrong size information.

> > *). Per namespace expectations. This is for similar reasons to the need
> > for multiple hashtables, though I haven't poked at that.
> 
> Expectation cache is not SLAB_DESTROY_BY_RCU, so the logic doesn't
> apply, I hope.

I'm not sure, I didn't poke at that much yet. But hashtables certainly
need fixing unless you can point out where I'm wrong.

> > I also think it is necessary to expose net namespace layout
> 
> Not necessary. Why?

How am I as a sysadmin supposed to figure out which net namespaces exist
on my system, and as a developer, supposed to debug these situations?

Jon.


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