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    Subject[LOCKDEP BUG][2.6.36-rc1] xt_info_wrlock?
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    Date
    Hi, I hit this when booting 2.6.36-rc1:

    =================================
    [ INFO: inconsistent lock state ]
    2.6.36-rc1 #2937
    ---------------------------------
    inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
    ifup-eth/3288 [HC0[0]:SC1[2]:HE1:SE0] takes:
    (&(&lock->lock)->rlock){+.?...}, at: [<ffffffffa0166eef>] ip6t_do_table+0x8a/0x3f1 [ip6_tables]
    {SOFTIRQ-ON-W} state was registered at:
    [<ffffffff8107b08e>] __lock_acquire+0x756/0x93c
    [<ffffffff8107b374>] lock_acquire+0x100/0x12d
    [<ffffffff813f4ec3>] _raw_spin_lock+0x40/0x73
    [<ffffffffa01664b1>] get_counters+0xb2/0x168 [ip6_tables]
    [<ffffffffa01665a3>] alloc_counters+0x3c/0x47 [ip6_tables]
    [<ffffffffa0167a7b>] do_ip6t_get_ctl+0x10c/0x363 [ip6_tables]
    [<ffffffff813863a2>] nf_sockopt+0x5a/0x86
    [<ffffffff813863e6>] nf_getsockopt+0x18/0x1a
    [<ffffffffa034c1ff>] ipv6_getsockopt+0x84/0xba [ipv6]
    [<ffffffffa0353289>] rawv6_getsockopt+0x42/0x4b [ipv6]
    [<ffffffff81355571>] sock_common_getsockopt+0x14/0x16
    [<ffffffff813525bb>] sys_getsockopt+0x7a/0x9b
    [<ffffffff8100ad32>] system_call_fastpath+0x16/0x1b
    irq event stamp: 40
    hardirqs last enabled at (40): [<ffffffff813f5ad5>] _raw_spin_unlock_irqrestore+0x47/0x79
    hardirqs last disabled at (39): [<ffffffff813f5036>] _raw_spin_lock_irqsave+0x2b/0x92
    softirqs last enabled at (0): [<ffffffff8104975a>] copy_process+0x40e/0x11ce
    softirqs last disabled at (9): [<ffffffff8100bc9c>] call_softirq+0x1c/0x30

    other info that might help us debug this:
    3 locks held by ifup-eth/3288:
    #0: (&idev->mc_ifc_timer){+.-...}, at: [<ffffffff8105841c>] run_timer_softirq+0x1f5/0x3e6
    #1: (rcu_read_lock){.+.+..}, at: [<ffffffffa03578ca>] mld_sendpack+0x0/0x3ab [ipv6]
    #2: (rcu_read_lock){.+.+..}, at: [<ffffffff81384f83>] nf_hook_slow+0x0/0x119

    stack backtrace:
    Pid: 3288, comm: ifup-eth Not tainted 2.6.36-rc1 #2937
    Call Trace:
    <IRQ> [<ffffffff81077ae6>] print_usage_bug+0x1a4/0x1b5
    [<ffffffff810164fa>] ? save_stack_trace+0x2f/0x4c
    [<ffffffff8106cd0c>] ? local_clock+0x40/0x59
    [<ffffffff810786b6>] ? check_usage_forwards+0x0/0xcf
    [<ffffffff81077de1>] mark_lock+0x2ea/0x51f
    [<ffffffff8107b014>] __lock_acquire+0x6dc/0x93c
    [<ffffffff8106cd0c>] ? local_clock+0x40/0x59
    [<ffffffffa0166eef>] ? ip6t_do_table+0x8a/0x3f1 [ip6_tables]
    [<ffffffff8107b374>] lock_acquire+0x100/0x12d
    [<ffffffffa0166eef>] ? ip6t_do_table+0x8a/0x3f1 [ip6_tables]
    [<ffffffff81011149>] ? sched_clock+0x9/0xd
    [<ffffffff813f4ec3>] _raw_spin_lock+0x40/0x73
    [<ffffffffa0166eef>] ? ip6t_do_table+0x8a/0x3f1 [ip6_tables]
    [<ffffffffa0166eef>] ip6t_do_table+0x8a/0x3f1 [ip6_tables]
    [<ffffffff810771db>] ? trace_hardirqs_off_caller+0x1f/0x9e
    [<ffffffff81384f83>] ? nf_hook_slow+0x0/0x119
    [<ffffffffa010601c>] ip6table_filter_hook+0x1c/0x20 [ip6table_filter]
    [<ffffffff81384f40>] nf_iterate+0x46/0x89
    [<ffffffffa035627b>] ? dst_output+0x0/0x5c [ipv6]
    [<ffffffff8138501b>] nf_hook_slow+0x98/0x119
    [<ffffffffa035627b>] ? dst_output+0x0/0x5c [ipv6]
    [<ffffffffa0349557>] ? icmp6_dst_alloc+0x0/0x1b2 [ipv6]
    [<ffffffffa0357b01>] mld_sendpack+0x237/0x3ab [ipv6]
    [<ffffffff81051475>] ? local_bh_enable_ip+0xc7/0xeb
    [<ffffffffa0358390>] mld_ifc_timer_expire+0x254/0x28d [ipv6]
    [<ffffffff810584ed>] run_timer_softirq+0x2c6/0x3e6
    [<ffffffff8105841c>] ? run_timer_softirq+0x1f5/0x3e6
    [<ffffffffa035813c>] ? mld_ifc_timer_expire+0x0/0x28d [ipv6]
    [<ffffffff8105169e>] ? __do_softirq+0x79/0x247
    [<ffffffff81051763>] __do_softirq+0x13e/0x247
    [<ffffffff8100bc9c>] call_softirq+0x1c/0x30
    [<ffffffff8100d32f>] do_softirq+0x4b/0xa3
    [<ffffffff8105120a>] irq_exit+0x4a/0x95
    [<ffffffff813fc185>] smp_apic_timer_interrupt+0x8c/0x9a
    [<ffffffff8100b753>] apic_timer_interrupt+0x13/0x20
    <EOI> [<ffffffff8102c72a>] ? native_flush_tlb_global+0x2b/0x32
    [<ffffffff81031fec>] kernel_map_pages+0x12c/0x142
    [<ffffffff810cc89a>] free_pages_prepare+0x14c/0x15d
    [<ffffffff810cc9c8>] free_hot_cold_page+0x2d/0x165
    [<ffffffff810ccb2b>] __free_pages+0x2b/0x34
    [<ffffffff810ccb7d>] free_pages+0x49/0x4e
    [<ffffffff81033871>] pgd_free+0x71/0x79
    [<ffffffff81048b1b>] __mmdrop+0x27/0x54
    [<ffffffff81042c62>] finish_task_switch+0xb4/0xe4
    [<ffffffff81042bae>] ? finish_task_switch+0x0/0xe4
    [<ffffffff810096e7>] ? __switch_to+0x1a9/0x297
    [<ffffffff81042df3>] schedule_tail+0x30/0xa7
    [<ffffffff8100ac33>] ret_from_fork+0x13/0x80

    I noticed in net/ipv6/netfilter/ip6_tables.c in get_counters() as with
    other "get_counters()" functions do not block bottom halves anymore as
    to this commit:

    commit 24b36f0193467fa727b85b4c004016a8dae999b9
    Author: Eric Dumazet <eric.dumazet@gmail.com>
    Date: Mon Aug 2 16:49:01 2010 +0200

    netfilter: {ip,ip6,arp}_tables: dont block bottom half more than necessary

    We currently disable BH for the whole duration of get_counters()

    Now we take xt_info_wrlock(cpu) lock out of BH disabling. And that lock
    even has the following comment:

    /*
    * The "writer" side needs to get exclusive access to the lock,
    * regardless of readers. This must be called with bottom half
    * processing (and thus also preemption) disabled.
    */
    static inline void xt_info_wrlock(unsigned int cpu)


    As lockdep has proven, this is not satisfied.

    -- Steve




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