Re: (spurious?) lockdep warning on Xen boot

[Peter Zijlstra]

On Mon, 2009-02-16 at 14:49 -0800, Jeremy Fitzhardinge wrote:
> I've been seeing this warning appear early when I boot under Xen:
> 
> ------------[ cut here ]------------
> WARNING: at /home/jeremy/git/linux/kernel/lockdep.c:2185 trace_hardirqs_on_caller+0xbc/0x13c()
> Modules linked in:
> Pid: 0, comm: swapper Not tainted 2.6.29-rc4-tip #12
> Call Trace:
>  [<ffffffff8023da44>] warn_slowpath+0xd8/0x114
>  [<ffffffff8020e9f9>] ? __raw_callee_save_xen_save_fl+0x11/0x1e
>  [<ffffffff8020b882>] ? xen_mc_flush+0x1e2/0x21b
>  [<ffffffff8025d424>] ? trace_hardirqs_off_caller+0x2e/0x8c
>  [<ffffffff8025e26b>] ? trace_hardirqs_off+0xd/0xf
>  [<ffffffff80705c2c>] ? xen_setup_kernel_pagetable+0x442/0x4a4
>  [<ffffffff8025f9d5>] trace_hardirqs_on_caller+0xbc/0x13c
>  [<ffffffff8025fa62>] trace_hardirqs_on+0xd/0xf
>  [<ffffffff80705c2c>] xen_setup_kernel_pagetable+0x442/0x4a4
>  [<ffffffff80704d91>] xen_start_kernel+0x34e/0x4da
> ---[ end trace 4eaa2a86a8e2da22 ]---
> 
> 
> Which corresponds to:
> 
> 	if (DEBUG_LOCKS_WARN_ON(unlikely(!early_boot_irqs_enabled)))
> 		return;
> 
> 
> The code in question is running before start_kernel, and ends up doing 
> some local_irq_save(flags)/local_irq_restore(flags) calls, which result 
> in interrupts being re-enabled.

I'm not too familiar with the early boot code, but the
early_boot_irqs_*() annotation is used to ensure IRQs are not enabled
too early.

You seem to do that, but I can't say what effect this would have on
early boot integrity.

Also, local_irq_save()/local_irq_restore() pairs should never re-enable
interrupts if they were off to begin with.

> I tried two approaches to fixing this.  One was to disable interrupts 
> early, before calling anything that would try to change the interrupt 
> state (which seems sane, since I guess head.S enters the kernel with 
> interrupts disabled), and the other was to call early_boot_irqs_on() to 
> suppress the warning.

Right, so you are saying you started out with IRQs enabled, and the
above local_irq_restore() would simply be the first irq-op to re-enable
it and goes splat.

In which case your disabled from beginning 'fix' looks like the right
thing to do.

> Both cleared up the quoted warning, but then I got a huge lump of 
> lockdep spew which seemed to be as a result of an interaction between 
> usb and swiotlb via Xen (quoted below).  I'm not sure if this is a real 
> report, or fallout from something going wrong in the early init stages 
> of lockdep.
> 
>   And if this second 
> warning is real, why does it get suppressed by the first warning?

Any lockdep warning disables lockdep for the simple reason that our lock
state cannot be trusted anymore, so by triggering something, any
potential trouble further down the line will be hidden.

> Or perhaps the second warning is real; in which case, where does the 
> problem lie? (I guess another case of being bitten by calling 
> __purge_vmap_area_lazy from interrupt context.)

Looks like a real problem, and yes your suggestion makes sense.

> Thanks,
>     J
> 
> /home/jeremy/git/linux/drivers/usb/core/inode.c: creating file '001'
> xen: registering gsi 18 triggering 0 polarity 1
> usb 1-3: new high speed USB device using ehci_hcd and address 2
> 
> ======================================================
> [ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
> 2.6.29-rc5-tip #22
> ------------------------------------------------------
> khubd/158 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
>  (&retval->lock){......}, at: [<ffffffff802a89b8>] dma_pool_alloc+0x30/0x29d
> 
> and this task is already holding:
>  (&ehci->lock){-.....}, at: [<ffffffff80464ba4>] ehci_urb_enqueue+0xab/0xe96
> which would create a new lock dependency:
>  (&ehci->lock){-.....} -> (&retval->lock){......}
> 
> but this new dependency connects a HARDIRQ-irq-safe lock:
>  (&ehci->lock){-.....}
> .... which became HARDIRQ-irq-safe at:
>   [<ffffffffffffffff>] 0xffffffffffffffff
> 
> to a HARDIRQ-irq-unsafe lock:
>  (purge_lock){+.+...}
> .... which became HARDIRQ-irq-unsafe at:
> ....  [<ffffffff80262dd9>] __lock_acquire+0x77d/0x16d9
>   [<ffffffff80263d96>] lock_acquire+0x61/0x84
>   [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>   [<ffffffff802a2c62>] __purge_vmap_area_lazy+0x50/0x1a8
>   [<ffffffff802a4485>] vm_unmap_aliases+0x1a9/0x1b8
>   [<ffffffff8020d1fa>] xen_create_contiguous_region+0x49/0xef
>   [<ffffffff803d867b>] xen_swiotlb_fixup+0x97/0xd0
>   [<ffffffff80716637>] swiotlb_alloc_boot+0x3e/0x49
>   [<ffffffff8071fe3e>] swiotlb_init_with_default_size+0x3c/0x120
>   [<ffffffff8071ff30>] swiotlb_init+0xe/0x10
>   [<ffffffff807165ec>] pci_swiotlb_init+0x6f/0x7c
>   [<ffffffff8070d4f5>] pci_iommu_alloc+0x59/0x5d
>   [<ffffffff807179d8>] mem_init+0xd/0xb7
>   [<ffffffff80705cb5>] start_kernel+0x3c0/0x452
>   [<ffffffff807052bf>] x86_64_start_reservations+0xaa/0xae
>   [<ffffffff80708f27>] xen_start_kernel+0x4e4/0x4eb
>   [<ffffffffffffffff>] 0xffffffffffffffff
> 
> other info that might help us debug this:
> 
> 2 locks held by khubd/158:
>  #0:  (usb_address0_mutex){+.+...}, at: [<ffffffff8044b51c>] hub_port_init+0x83/0x617
>  #1:  (&ehci->lock){-.....}, at: [<ffffffff80464ba4>] ehci_urb_enqueue+0xab/0xe96
> 
> the HARDIRQ-irq-safe lock's dependencies:
> -> (&ehci->lock){-.....} ops: 0 {
>    IN-HARDIRQ-W at:
>                         [<ffffffffffffffff>] 0xffffffffffffffff
>    INITIAL USE at:
>                        [<ffffffffffffffff>] 0xffffffffffffffff
>  }
>  ... key      at: [<ffffffff80ecb800>] __key.31741+0x0/0x8
>  -> (hcd_urb_list_lock){......} ops: 0 {
>     INITIAL USE at:
>                          [<ffffffff80262e6b>] __lock_acquire+0x80f/0x16d9
>                          [<ffffffff80263d96>] lock_acquire+0x61/0x84
>                          [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>                          [<ffffffff8044f3d7>] usb_hcd_link_urb_to_ep+0x28/0xab
>                          [<ffffffff804506bb>] usb_hcd_submit_urb+0x460/0xa8a
>                          [<ffffffff80451333>] usb_submit_urb+0x2f8/0x315
>                          [<ffffffff80452568>] usb_start_wait_urb+0x56/0x17b
>                          [<ffffffff80452893>] usb_control_msg+0xd4/0xf6
>                          [<ffffffff804537b8>] usb_get_descriptor+0x76/0xa6
>                          [<ffffffff80453841>] usb_get_device_descriptor+0x59/0x88
>                          [<ffffffff804500ae>] usb_add_hcd+0x4ad/0x64a
>                          [<ffffffff8045b347>] usb_hcd_pci_probe+0x25c/0x30d
>                          [<ffffffff803d3935>] local_pci_probe+0x17/0x1b
>                          [<ffffffff803d406d>] pci_device_probe+0x61/0x8b
>                          [<ffffffff80440e0e>] driver_probe_device+0xc9/0x177
>                          [<ffffffff80440f23>] __driver_attach+0x67/0x91
>                          [<ffffffff8044065f>] bus_for_each_dev+0x57/0x91
>                          [<ffffffff80440c46>] driver_attach+0x21/0x23
>                          [<ffffffff8043ff33>] bus_add_driver+0xbf/0x20c
>                          [<ffffffff8044113a>] driver_register+0xb0/0x130
>                          [<ffffffff803d4328>] __pci_register_driver+0x68/0xa0
>                          [<ffffffff80725d66>] ehci_hcd_init+0xb8/0xe3
>                          [<ffffffff8020a066>] do_one_initcall+0x5b/0x13e
>                          [<ffffffff80705659>] kernel_init+0x134/0x18c
>                          [<ffffffff8021360a>] child_rip+0xa/0x20
>                          [<ffffffffffffffff>] 0xffffffffffffffff
>   }
>   ... key      at: [<ffffffff806b32d8>] hcd_urb_list_lock+0x18/0x30
>  ... acquired at:
>    [<ffffffff802639b0>] __lock_acquire+0x1354/0x16d9
>    [<ffffffff80263d96>] lock_acquire+0x61/0x84
>    [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>    [<ffffffff8044f3d7>] usb_hcd_link_urb_to_ep+0x28/0xab
>    [<ffffffff80464bcd>] ehci_urb_enqueue+0xd4/0xe96
>    [<ffffffff80450c0b>] usb_hcd_submit_urb+0x9b0/0xa8a
>    [<ffffffff80451333>] usb_submit_urb+0x2f8/0x315
>    [<ffffffff80452568>] usb_start_wait_urb+0x56/0x17b
>    [<ffffffff80452893>] usb_control_msg+0xd4/0xf6
>    [<ffffffff8044b730>] hub_port_init+0x297/0x617
>    [<ffffffff8044e0f8>] hub_thread+0xae5/0x1295
>    [<ffffffff802540e2>] kthread+0x4e/0x7b
>    [<ffffffff8021360a>] child_rip+0xa/0x20
>    [<ffffffffffffffff>] 0xffffffffffffffff
> 
> 
> the HARDIRQ-irq-unsafe lock's dependencies:
> -> (purge_lock){+.+...} ops: 0 {
>    HARDIRQ-ON-W at:
>                         [<ffffffff80262dd9>] __lock_acquire+0x77d/0x16d9
>                         [<ffffffff80263d96>] lock_acquire+0x61/0x84
>                         [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>                         [<ffffffff802a2c62>] __purge_vmap_area_lazy+0x50/0x1a8
>                         [<ffffffff802a4485>] vm_unmap_aliases+0x1a9/0x1b8
>                         [<ffffffff8020d1fa>] xen_create_contiguous_region+0x49/0xef
>                         [<ffffffff803d867b>] xen_swiotlb_fixup+0x97/0xd0
>                         [<ffffffff80716637>] swiotlb_alloc_boot+0x3e/0x49
>                         [<ffffffff8071fe3e>] swiotlb_init_with_default_size+0x3c/0x120
>                         [<ffffffff8071ff30>] swiotlb_init+0xe/0x10
>                         [<ffffffff807165ec>] pci_swiotlb_init+0x6f/0x7c
>                         [<ffffffff8070d4f5>] pci_iommu_alloc+0x59/0x5d
>                         [<ffffffff807179d8>] mem_init+0xd/0xb7
>                         [<ffffffff80705cb5>] start_kernel+0x3c0/0x452
>                         [<ffffffff807052bf>] x86_64_start_reservations+0xaa/0xae
>                         [<ffffffff80708f27>] xen_start_kernel+0x4e4/0x4eb
>                         [<ffffffffffffffff>] 0xffffffffffffffff
>    SOFTIRQ-ON-W at:
>                         [<ffffffff80262e02>] __lock_acquire+0x7a6/0x16d9
>                         [<ffffffff80263d96>] lock_acquire+0x61/0x84
>                         [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>                         [<ffffffff802a2c62>] __purge_vmap_area_lazy+0x50/0x1a8
>                         [<ffffffff802a4485>] vm_unmap_aliases+0x1a9/0x1b8
>                         [<ffffffff8020d1fa>] xen_create_contiguous_region+0x49/0xef
>                         [<ffffffff803d867b>] xen_swiotlb_fixup+0x97/0xd0
>                         [<ffffffff80716637>] swiotlb_alloc_boot+0x3e/0x49
>                         [<ffffffff8071fe3e>] swiotlb_init_with_default_size+0x3c/0x120
>                         [<ffffffff8071ff30>] swiotlb_init+0xe/0x10
>                         [<ffffffff807165ec>] pci_swiotlb_init+0x6f/0x7c
>                         [<ffffffff8070d4f5>] pci_iommu_alloc+0x59/0x5d
>                         [<ffffffff807179d8>] mem_init+0xd/0xb7
>                         [<ffffffff80705cb5>] start_kernel+0x3c0/0x452
>                         [<ffffffff807052bf>] x86_64_start_reservations+0xaa/0xae
>                         [<ffffffff80708f27>] xen_start_kernel+0x4e4/0x4eb
>                         [<ffffffffffffffff>] 0xffffffffffffffff
>    INITIAL USE at:
>                        [<ffffffff80262e6b>] __lock_acquire+0x80f/0x16d9
>                        [<ffffffff80263d96>] lock_acquire+0x61/0x84
>                        [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>                        [<ffffffff802a2c62>] __purge_vmap_area_lazy+0x50/0x1a8
>                        [<ffffffff802a4485>] vm_unmap_aliases+0x1a9/0x1b8
>                        [<ffffffff8020d1fa>] xen_create_contiguous_region+0x49/0xef
>                        [<ffffffff803d867b>] xen_swiotlb_fixup+0x97/0xd0
>                        [<ffffffff80716637>] swiotlb_alloc_boot+0x3e/0x49
>                        [<ffffffff8071fe3e>] swiotlb_init_with_default_size+0x3c/0x120
>                        [<ffffffff8071ff30>] swiotlb_init+0xe/0x10
>                        [<ffffffff807165ec>] pci_swiotlb_init+0x6f/0x7c
>                        [<ffffffff8070d4f5>] pci_iommu_alloc+0x59/0x5d
>                        [<ffffffff807179d8>] mem_init+0xd/0xb7
>                        [<ffffffff80705cb5>] start_kernel+0x3c0/0x452
>                        [<ffffffff807052bf>] x86_64_start_reservations+0xaa/0xae
>                        [<ffffffff80708f27>] xen_start_kernel+0x4e4/0x4eb
>                        [<ffffffffffffffff>] 0xffffffffffffffff
>  }
>  ... key      at: [<ffffffff806962b8>] purge_lock.24514+0x18/0x30
>  -> (vmap_area_lock){+.+...} ops: 0 {
>     HARDIRQ-ON-W at:
>                           [<ffffffff80262dd9>] __lock_acquire+0x77d/0x16d9
>                           [<ffffffff80263d96>] lock_acquire+0x61/0x84
>                           [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>                           [<ffffffff802a2f25>] alloc_vmap_area+0x99/0x1ca
>                           [<ffffffff802a3133>] __get_vm_area_node+0xdd/0x18d
>                           [<ffffffff802a324d>] get_vm_area_caller+0x34/0x36
>                           [<ffffffff802a3bee>] vmap+0x36/0x66
>                           [<ffffffff8021819e>] text_poke+0x11c/0x1b2
>                           [<ffffffff80218283>] alternatives_smp_unlock+0x4f/0x67
>                           [<ffffffff80218514>] alternatives_smp_switch+0x15f/0x19e
>                           [<ffffffff8070d71b>] alternative_instructions+0xf2/0x131
>                           [<ffffffff8070df1f>] check_bugs+0xe/0x2d
>                           [<ffffffff80705d2b>] start_kernel+0x436/0x452
>                           [<ffffffff807052bf>] x86_64_start_reservations+0xaa/0xae
>                           [<ffffffff80708f27>] xen_start_kernel+0x4e4/0x4eb
>                           [<ffffffffffffffff>] 0xffffffffffffffff
>     SOFTIRQ-ON-W at:
>                           [<ffffffff80262e02>] __lock_acquire+0x7a6/0x16d9
>                           [<ffffffff80263d96>] lock_acquire+0x61/0x84
>                           [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>                           [<ffffffff802a2f25>] alloc_vmap_area+0x99/0x1ca
>                           [<ffffffff802a3133>] __get_vm_area_node+0xdd/0x18d
>                           [<ffffffff802a324d>] get_vm_area_caller+0x34/0x36
>                           [<ffffffff802a3bee>] vmap+0x36/0x66
>                           [<ffffffff8021819e>] text_poke+0x11c/0x1b2
>                           [<ffffffff80218283>] alternatives_smp_unlock+0x4f/0x67
>                           [<ffffffff80218514>] alternatives_smp_switch+0x15f/0x19e
>                           [<ffffffff8070d71b>] alternative_instructions+0xf2/0x131
>                           [<ffffffff8070df1f>] check_bugs+0xe/0x2d
>                           [<ffffffff80705d2b>] start_kernel+0x436/0x452
>                           [<ffffffff807052bf>] x86_64_start_reservations+0xaa/0xae
>                           [<ffffffff80708f27>] xen_start_kernel+0x4e4/0x4eb
>                           [<ffffffffffffffff>] 0xffffffffffffffff
>     INITIAL USE at:
>                          [<ffffffff80262e6b>] __lock_acquire+0x80f/0x16d9
>                          [<ffffffff80263d96>] lock_acquire+0x61/0x84
>                          [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>                          [<ffffffff802a2f25>] alloc_vmap_area+0x99/0x1ca
>                          [<ffffffff802a3133>] __get_vm_area_node+0xdd/0x18d
>                          [<ffffffff802a324d>] get_vm_area_caller+0x34/0x36
>                          [<ffffffff802a3bee>] vmap+0x36/0x66
>                          [<ffffffff8021819e>] text_poke+0x11c/0x1b2
>                          [<ffffffff80218283>] alternatives_smp_unlock+0x4f/0x67
>                          [<ffffffff80218514>] alternatives_smp_switch+0x15f/0x19e
>                          [<ffffffff8070d71b>] alternative_instructions+0xf2/0x131
>                          [<ffffffff8070df1f>] check_bugs+0xe/0x2d
>                          [<ffffffff80705d2b>] start_kernel+0x436/0x452
>                          [<ffffffff807052bf>] x86_64_start_reservations+0xaa/0xae
>                          [<ffffffff80708f27>] xen_start_kernel+0x4e4/0x4eb
>                          [<ffffffffffffffff>] 0xffffffffffffffff
>   }
>   ... key      at: [<ffffffff80696278>] vmap_area_lock+0x18/0x30
>  ... acquired at:
>    [<ffffffff802639b0>] __lock_acquire+0x1354/0x16d9
>    [<ffffffff80263d96>] lock_acquire+0x61/0x84
>    [<ffffffff8053092c>] _spin_lock+0x31/0x3d
>    [<ffffffff802a2d69>] __purge_vmap_area_lazy+0x157/0x1a8
>    [<ffffffff802a4485>] vm_unmap_aliases+0x1a9/0x1b8
>    [<ffffffff8020e190>] xen_alloc_ptpage+0xa8/0xd9
>    [<ffffffff8020e1fe>] xen_alloc_pte+0x13/0x15
>    [<ffffffff8029947c>] __pte_alloc_kernel+0x5b/0xb1
>    [<ffffffff802a36f5>] vmap_page_range+0x19b/0x30f
>    [<ffffffff802a389b>] map_vm_area+0x32/0x46
>    [<ffffffff802a3c05>] vmap+0x4d/0x66
>    [<ffffffff8021819e>] text_poke+0x11c/0x1b2
>    [<ffffffff80218283>] alternatives_smp_unlock+0x4f/0x67
>    [<ffffffff80218514>] alternatives_smp_switch+0x15f/0x19e
>    [<ffffffff8070d71b>] alternative_instructions+0xf2/0x131
>    [<ffffffff8070df1f>] check_bugs+0xe/0x2d
>    [<ffffffff80705d2b>] start_kernel+0x436/0x452
>    [<ffffffff807052bf>] x86_64_start_reservations+0xaa/0xae
>    [<ffffffff80708f27>] xen_start_kernel+0x4e4/0x4eb
>    [<ffffffffffffffff>] 0xffffffffffffffff
> 
>  -> (&q->lock#2){-.....} ops: 0 {
>     IN-HARDIRQ-W at:
>                           [<ffffffffffffffff>] 0xffffffffffffffff
>     INITIAL USE at:
>                          [<ffffffff80262e6b>] __lock_acquire+0x80f/0x16d9
>                          [<ffffffff80263d96>] lock_acquire+0x61/0x84
>                          [<ffffffff80530a0a>] _spin_lock_irqsave+0x47/0x5b
>                          [<ffffffff80268591>] generic_exec_single+0x41/0x8f
>                          [<ffffffff80268735>] smp_call_function_single+0x10e/0x127
>                          [<ffffffff80268813>] smp_call_function_many+0xc5/0x1f8
>                          [<ffffffff8026896b>] smp_call_function+0x25/0x29
>                          [<ffffffff80244ee0>] on_each_cpu+0x1d/0x48
>                          [<ffffffff802ada09>] kmem_cache_shrink+0x5a/0x1c8
>                          [<ffffffff803dc219>] acpi_os_purge_cache+0xe/0x12
>                          [<ffffffff803f4ac5>] acpi_purge_cached_objects+0x15/0x3d
>                          [<ffffffff803f4b55>] acpi_initialize_objects+0x4e/0x59
>                          [<ffffffff80721660>] acpi_init+0x91/0x234
>                          [<ffffffff8020a066>] do_one_initcall+0x5b/0x13e
>                          [<ffffffff80705659>] kernel_init+0x134/0x18c
>                          [<ffffffff8021360a>] child_rip+0xa/0x20
>                          [<ffffffffffffffff>] 0xffffffffffffffff
>   }
>   ... key      at: [<ffffffff80e72e60>] __key.12205+0x0/0x8
>  ... acquired at:
>    [<ffffffff802639b0>] __lock_acquire+0x1354/0x16d9
>    [<ffffffff80263d96>] lock_acquire+0x61/0x84
>    [<ffffffff80530a0a>] _spin_lock_irqsave+0x47/0x5b
>    [<ffffffff80268591>] generic_exec_single+0x41/0x8f
>    [<ffffffff80268735>] smp_call_function_single+0x10e/0x127
>    [<ffffffff80268813>] smp_call_function_many+0xc5/0x1f8
>    [<ffffffff8026896b>] smp_call_function+0x25/0x29
>    [<ffffffff80244ee0>] on_each_cpu+0x1d/0x48
>    [<ffffffff80230f58>] flush_tlb_all+0x1c/0x1e
>    [<ffffffff802a2d54>] __purge_vmap_area_lazy+0x142/0x1a8
>    [<ffffffff802a4485>] vm_unmap_aliases+0x1a9/0x1b8
>    [<ffffffff8020d83d>] __xen_pgd_pin+0x1d/0x19d
>    [<ffffffff8020da1e>] xen_activate_mm+0x2a/0x37
>    [<ffffffff802b4c88>] flush_old_exec+0x32d/0x72c
>    [<ffffffff802e7853>] load_elf_binary+0x397/0x1940
>    [<ffffffff802b473a>] search_binary_handler+0xbc/0x261
>    [<ffffffff802b594a>] do_execve+0x1b9/0x269
>    [<ffffffff80210a14>] sys_execve+0x43/0x65
>    [<ffffffff80213688>] kernel_execve+0x68/0xd0
>    [<ffffffff8021360a>] child_rip+0xa/0x20
>    [<ffffffffffffffff>] 0xffffffffffffffff
> 
> 
> stack backtrace:
> Pid: 158, comm: khubd Not tainted 2.6.29-rc5-tip #22
> Call Trace:
>  [<ffffffff80262586>] check_usage+0x3d6/0x3e7
>  [<ffffffff802620ab>] ? check_noncircular+0xe8/0x11d
>  [<ffffffff802625f8>] check_irq_usage+0x61/0xc5
>  [<ffffffff802636ea>] __lock_acquire+0x108e/0x16d9
>  [<ffffffff802165fe>] ? print_context_stack+0xf8/0x116
>  [<ffffffff8021577e>] ? dump_trace+0x265/0x277
>  [<ffffffff80263d96>] lock_acquire+0x61/0x84
>  [<ffffffff802a89b8>] ? dma_pool_alloc+0x30/0x29d
>  [<ffffffff80530a0a>] _spin_lock_irqsave+0x47/0x5b
>  [<ffffffff802a89b8>] ? dma_pool_alloc+0x30/0x29d
>  [<ffffffff802a89b8>] dma_pool_alloc+0x30/0x29d
>  [<ffffffff80263c52>] ? __lock_acquire+0x15f6/0x16d9
>  [<ffffffff80263c52>] ? __lock_acquire+0x15f6/0x16d9
>  [<ffffffff80464163>] ehci_qh_alloc+0x28/0xbd
>  [<ffffffff8020f132>] ? check_events+0x12/0x20
>  [<ffffffff8020f11f>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff80464237>] qh_append_tds+0x3f/0x581
>  [<ffffffff8020f11f>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff8026426b>] ? lock_release+0x164/0x171
>  [<ffffffff8020f11f>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff8044f3d7>] ? usb_hcd_link_urb_to_ep+0x28/0xab
>  [<ffffffff80464bf2>] ehci_urb_enqueue+0xf9/0xe96
>  [<ffffffff803c218f>] ? string+0x3d/0xa1
>  [<ffffffff803c2ac9>] ? vsnprintf+0x8d6/0x930
>  [<ffffffff8021577e>] ? dump_trace+0x265/0x277
>  [<ffffffff803d82b0>] ? xen_range_needs_mapping+0xe/0x10
>  [<ffffffff80229918>] ? swiotlb_arch_range_needs_mapping+0x19/0x1b
>  [<ffffffff80450c0b>] usb_hcd_submit_urb+0x9b0/0xa8a
>  [<ffffffff8020ea4d>] ? xen_force_evtchn_callback+0xd/0xf
>  [<ffffffff803cd8e3>] ? swiotlb_map_page+0x0/0x1a1
>  [<ffffffff8026026a>] ? lockdep_init_map+0x92/0x529
>  [<ffffffff8020f11f>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff80261ab2>] ? debug_check_no_locks_freed+0x13a/0x147
>  [<ffffffff80451333>] usb_submit_urb+0x2f8/0x315
>  [<ffffffff80452568>] usb_start_wait_urb+0x56/0x17b
>  [<ffffffff8020f132>] ? check_events+0x12/0x20
>  [<ffffffff80451710>] ? usb_init_urb+0x27/0x37
>  [<ffffffff80452893>] usb_control_msg+0xd4/0xf6
>  [<ffffffff802ac4af>] ? kmem_cache_alloc+0xc1/0xe5
>  [<ffffffff8044b730>] hub_port_init+0x297/0x617
>  [<ffffffff8044e0f8>] hub_thread+0xae5/0x1295
>  [<ffffffff80261976>] ? trace_hardirqs_on+0xd/0xf
>  [<ffffffff802544b6>] ? autoremove_wake_function+0x0/0x3d
>  [<ffffffff805307ef>] ? _spin_unlock_irqrestore+0x53/0x58
>  [<ffffffff8044d613>] ? hub_thread+0x0/0x1295
>  [<ffffffff8044d613>] ? hub_thread+0x0/0x1295
>  [<ffffffff802540e2>] kthread+0x4e/0x7b
>  [<ffffffff8021360a>] child_rip+0xa/0x20
>  [<ffffffff80212fd0>] ? restore_args+0x0/0x30
>  [<ffffffff8020f11f>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff8020f11f>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff8020f11f>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff80213600>] ? child_rip+0x0/0x20
> 
> 

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