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Subject: Re: PROBLEM: reproducible crash KVM+nf_conntrack all recent 2.6
 kernels
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Jon Masters <jonathan@jonmasters.org>
Cc: Patrick McHardy <kaber@trash.net>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       netdev <netdev@vger.kernel.org>, netfilter-devel@vger.kernel.org
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Date: Fri, 29 Jan 2010 10:10:32 +0100
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Le vendredi 29 janvier 2010 à 03:42 -0500, Jon Masters a écrit :
> Hi,
> 
> So I did some poking (still trying to figure out netfilter a little
> internally) and looked over the handling of connection tracking. The
> oops reports I have been getting generally lie in __nf_conntrack_find,
> specifically within a hlist iterator that looks up the information for
> the current connection in a per-net namespace hashtable (under RCU, it's
> been locked already by the time we get in here). Here's the piece:
> 
>         hlist_nulls_for_each_entry_rcu(h, n, &net->ct.hash[hash],
> hnnode) {
>                 if (nf_ct_tuple_equal(tuple, &h->tuple)) {
>                         NF_CT_STAT_INC(net, found);
>                         local_bh_enable();
>                         return h;
>                 }
>                 NF_CT_STAT_INC(net, searched);
>         }
> 
> Instrumenting the kernel at the moment and then setting up more of a
> debugging environment to poke at what goes wrong here. Perhaps there's
> some broken RCU assumption - I just spent the last few hours reading
> over netfilter source and Paul's RCU docs again to brush up.
> 
> Perhaps you netdev folks can let me know if there's a handy netfilter
> debugging guide somewhere.
> 
> Jon.
> 
> 

Jon, do you have multiple network namespace active on your machine, when
crash occurs ?


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