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    SubjectRe: [PATCH] netfilter: use per-cpu spinlock rather than RCU (v3)
    Jan Engelhardt wrote:
    > On Wednesday 2009-04-15 23:07, Eric Dumazet wrote:
    >> Stephen Hemminger a écrit :
    >>> Looks like there is some recursive path into ip_tables that makes the
    >>> per-cpu spinlock break. I get lockup's with KVM networking.
    >>>
    >>> Suggestions?
    >> Well, it seems original patch was not so bad after all
    >>
    >> http://lists.netfilter.org/pipermail/netfilter-devel/2006-January/023175.html
    >>
    >> So change per-cpu spinlocks to per-cpu rwlocks
    >>
    >> and use read_lock() in ipt_do_table() to allow recursion...
    >>
    > iptables cannot quite recurse into itself due to the comefrom stuff.

    Actually it can by using the REJECT target:

    > [ 2106.068550] [<ffffffff804b0195>] ? nf_hook_slow+0x89/0x104
    > [ 2106.068552] [<ffffffff804b8ed0>] ? dst_output+0x0/0xb
    > [ 2106.068555] [<ffffffff80393925>] ? _raw_spin_unlock+0x8b/0x92
    > [ 2106.068557] [<ffffffff804ba8c7>] ? __ip_local_out+0x98/0x9a
    > [ 2106.068559] [<ffffffff804ba8d2>] ? ip_local_out+0x9/0x1f
    > [ 2106.068562] [<ffffffff804babb4>] ? ip_push_pending_frames+0x2cc/0x33e
    > [ 2106.068566] [<ffffffff804dac79>] ? icmp_send+0x559/0x588
    > [ 2106.068569] [<ffffffff8022d3a0>] ? task_rq_lock+0x46/0x79
    > [ 2106.068571] [<ffffffff8023004f>] ? enqueue_task_fair+0x23b/0x293
    > [ 2106.068575] [<ffffffffa00f5083>] ? reject_tg+0x41/0x30e [ipt_REJECT]
    > [ 2106.068578] [<ffffffffa024084f>] ? ipt_do_table+0x534/0x5f1 [ip_tables]



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