netdev - Re: debug: nt_conntrack and KVM crash

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Date:	Sat, 30 Jan 2010 07:58:24 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jon Masters <jonathan@...masters.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: debug: nt_conntrack and KVM crash

Le vendredi 29 janvier 2010 à 20:59 -0500, Jon Masters a écrit :
> On Fri, 2010-01-29 at 20:57 -0500, Jon Masters wrote:
> 
> > Ah so I should have realized before but I wasn't looking at valid values
> > for the range of the hashtable yet, nf_conntrack_htable_size is getting
> > wildly out of whack. It goes from:
> > 
> > (gdb) print nf_conntrack_hash_rnd
> > $1 = 2688505299
> > (gdb) print nf_conntrack_htable_size
> > $2 = 16384
> > 
> > nf_conntrack_events: 1
> > nf_conntrack_max: 65536
> > 
> > Shortly after booting, before being NULLed shortly after starting some
> > virtual machines (the hash isn't reset, whereas it is recomputed if the
> > hashtable is re-initialized after an intentional resizing operation):
> 
> I mean the *seed* isn't changed, so I don't think it was resized
> intentionally. I wonder where else htable_size is fiddled with.
> 
> Jon.
> 
> 

This rings a bell here, since another crash analysis on another problem
suggested to me a potential problem with read_mostly and modules, but I
had no time to confirm the thing yet.

Could you try changing


net/netfilter/nf_conntrack_core.c:57:unsigned int nf_conntrack_htable_size __read_mostly;
to
net/netfilter/nf_conntrack_core.c:57:unsigned int nf_conntrack_htable_size ;



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