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    SubjectRe: PROBLEM: reproducible crash KVM+nf_conntrack all recent 2.6 kernels
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    Date
    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.




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