Re: PROBLEM: reproducible crash KVM+nf_conntrack all recent 2.6kernels

From: Eric Dumazet
Date: Fri Jan 29 2010 - 04:10:44 EST

Le vendredi 29 janvier 2010 Ã 03:42 -0500, Jon Masters a Ãcrit :
> 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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