Date:	Thu, 21 Aug 2014 20:52:09 +0200
From:	Benjamin Block <bebl@...eta.org>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: BUG: lockdep (inconsistent usage) in netlink

Hello,

while rebooting one of my dev-machines I stumbled over this
lockdep-mess-up:

> =================================
> [ INFO: inconsistent lock state ]
> 3.17.0-rc1-00001-gb83ca8c #2 Tainted: G           O  
> ---------------------------------
> inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
>  (&(&list->lock)->rlock#3){?.-...}, at: [<ffffffff819580db>] skb_queue_tail+0x2b/0x60
> {HARDIRQ-ON-W} state was registered at:
>   [<ffffffff8111c9f7>] __lock_acquire+0x877/0x1c90
>   [<ffffffff8111e45a>] lock_acquire+0xca/0x120
>   [<ffffffff81afc744>] _raw_spin_lock_bh+0x44/0x80
>   [<ffffffff819a8918>] netlink_poll+0xf8/0x1c0
>   [<ffffffff8194e031>] sock_poll+0x161/0x190
>   [<ffffffff81271ffb>] SyS_epoll_ctl+0x51b/0xd10
>   [<ffffffff81afd452>] system_call_fastpath+0x16/0x1b
> irq event stamp: 1699744
> hardirqs last  enabled at (1699741): [<ffffffff8189b1d4>] cpuidle_enter_state+0xc4/0x190
> hardirqs last disabled at (1699742): [<ffffffff81afdfaa>] common_interrupt+0x6a/0x6f
> softirqs last  enabled at (1699744): [<ffffffff810d7fda>] _local_bh_enable+0x4a/0x50
> softirqs last disabled at (1699743): [<ffffffff810d88f0>] irq_enter+0x30/0x70
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
>
>        CPU0
>        ----
>   lock(&(&list->lock)->rlock#3);
>   <Interrupt>
>     lock(&(&list->lock)->rlock#3);
>
>  *** DEADLOCK ***
>
> no locks held by swapper/0/0.
>
> stack backtrace:
> CPU: 0 PID: 0 Comm: swapper/0 Tainted: G           O   3.17.0-rc1-00001-gb83ca8c #2
> Hardware name: ASUS All Series/Q87T, BIOS 0216 10/16/2013
>  ffffffff8295a5b0 ffff8802158039a8 ffffffff81af20fa 0000000000000000
>  ffffffff822164e0 ffff880215803a08 ffffffff81aee400 0000000000000000
>  ffffffff00000000 ffff880200000001 ffffffff8105ac0f ffffffff82d2abe0
> Call Trace:
>  <IRQ>  [<ffffffff81af20fa>] dump_stack+0x4e/0x68
>  [<ffffffff81aee400>] print_usage_bug+0x1ec/0x1fd
>  [<ffffffff8105ac0f>] ? save_stack_trace+0x2f/0x50
>  [<ffffffff8111b600>] ? print_irq_inversion_bug+0x200/0x200
>  [<ffffffff8111c061>] mark_lock+0x191/0x2b0
>  [<ffffffff8111c96a>] __lock_acquire+0x7ea/0x1c90
>  [<ffffffff8111ca94>] ? __lock_acquire+0x914/0x1c90
>  [<ffffffff8111b600>] ? print_irq_inversion_bug+0x200/0x200
>  [<ffffffff8111ca94>] ? __lock_acquire+0x914/0x1c90
>  [<ffffffff8111e45a>] lock_acquire+0xca/0x120
>  [<ffffffff819580db>] ? skb_queue_tail+0x2b/0x60
>  [<ffffffff81afc590>] _raw_spin_lock_irqsave+0x50/0x90
>  [<ffffffff819580db>] ? skb_queue_tail+0x2b/0x60
>  [<ffffffff819580db>] skb_queue_tail+0x2b/0x60
>  [<ffffffff819a774f>] __netlink_sendskb+0x21f/0x250
>  [<ffffffff819a7d63>] netlink_broadcast_filtered+0x273/0x3b0
>  [<ffffffff819a7ebd>] netlink_broadcast+0x1d/0x20
>  [<ffffffff8152fb8a>] ? nla_reserve+0x2a/0x40
>  [<ffffffff81589728>] acpi_bus_generate_netlink_event+0x160/0x178
>  [<ffffffff815a8db9>] acpi_button_notify+0xe1/0xec
>  [<ffffffff81580648>] acpi_device_notify+0x19/0x1b
>  [<ffffffff81580662>] acpi_device_notify_fixed+0x18/0x1c
>  [<ffffffff8158f039>] acpi_ev_fixed_event_detect+0xe6/0x10d
>  [<ffffffff8159157a>] acpi_ev_sci_xrupt_handler+0x19/0x3f
>  [<ffffffff8157c1a9>] acpi_irq+0x16/0x31
>  [<ffffffff81131e2a>] handle_irq_event_percpu+0x6a/0x1d0
>  [<ffffffff81131fd8>] handle_irq_event+0x48/0x70
>  [<ffffffff8113534f>] ? handle_fasteoi_irq+0x2f/0x160
>  [<ffffffff811353e7>] handle_fasteoi_irq+0xc7/0x160
>  [<ffffffff8104cd94>] handle_irq+0x134/0x150
>  [<ffffffff810f4876>] ? atomic_notifier_call_chain+0x16/0x20
>  [<ffffffff81054dec>] ? __exit_idle+0x2c/0x30
>  [<ffffffff81affe7e>] do_IRQ+0x5e/0x100
>  [<ffffffff81afdfaf>] common_interrupt+0x6f/0x6f
>  <EOI>  [<ffffffff8189b1df>] ? cpuidle_enter_state+0xcf/0x190
>  [<ffffffff8189b1d4>] ? cpuidle_enter_state+0xc4/0x190
>  [<ffffffff8189b387>] cpuidle_enter+0x17/0x20
>  [<ffffffff81111ae1>] cpu_startup_entry+0x3a1/0x3c0
>  [<ffffffff81ae92a4>] rest_init+0xc4/0xd0
>  [<ffffffff81ae91e5>] ? rest_init+0x5/0xd0
>  [<ffffffff825718a1>] ? ftrace_init+0xa8/0x13b
>  [<ffffffff8255103a>] start_kernel+0x461/0x46e
>  [<ffffffff82550939>] ? set_init_arg+0x57/0x57
>  [<ffffffff825505af>] x86_64_start_reservations+0x2a/0x2c
>  [<ffffffff825506ae>] x86_64_start_kernel+0xfd/0x101

Sadly I couldn't reproduce it. This looks all to be very general
functions and my best guess is, netlink_poll() needs to be irq-save.
Thing is, the corresponding code is quite old and I can't really bisec
it, because the none-reproducibility.

There is only the small ipv6-fib patch applied, I send in earlier today
(https://lkml.org/lkml/2014/8/21/506). This should have nothing to do
with this here.

-- 
If a listener nods his head when you're explaining your program, wake him up.
--
                                                          best regards,
                                                            - Benjamin Block

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