I've been trying to use the Hyper-V balloon driver to allow the host to
reclaim unused memory but have been hitting issues. With a Hyper-V 2012
R2 guest with 4GBytes of RAM, dynamic memory on, 1GByte minimum 10GByte
maximum, 8 vcpus, running a 3.18.0-rc3 kernel with no swap configured
the following lockdep splat occurred:
=================================
[ INFO: inconsistent lock state ]
3.18.0-rc3.x86_64 #159 Not tainted
---------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
swapper/0/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
(bdev_lock){+.?...}, at: [<ffffffff811ff39c>] nr_blockdev_pages+0x1c/0x80
{SOFTIRQ-ON-W} state was registered at:
[<ffffffff810ba03d>] __lock_acquire+0x87d/0x1c60
[<ffffffff810bbcdc>] lock_acquire+0xfc/0x150
[<ffffffff816e4019>] _raw_spin_lock+0x39/0x50
[<ffffffff811ff39c>] nr_blockdev_pages+0x1c/0x80
[<ffffffff8115d5f7>] si_meminfo+0x47/0x70
[<ffffffff81d6622f>] eventpoll_init+0x11/0x10a
[<ffffffff81d3d150>] do_one_initcall+0xf9/0x1a7
[<ffffffff81d3d3d2>] kernel_init_freeable+0x1d4/0x268
[<ffffffff816ce0ae>] kernel_init+0xe/0x100
[<ffffffff816e4dfc>] ret_from_fork+0x7c/0xb0
irq event stamp: 2660283708
hardirqs last enabled at (2660283708): [<ffffffff8115eef5>] free_hot_cold_page+0x175/0x190
hardirqs last disabled at (2660283707): [<ffffffff8115ee25>] free_hot_cold_page+0xa5/0x190
softirqs last enabled at (2660132034): [<ffffffff81071e6a>] _local_bh_enable+0x4a/0x50
softirqs last disabled at (2660132035): [<ffffffff81072478>] irq_exit+0x58/0xc0
might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(bdev_lock);
<Interrupt>
lock(bdev_lock);
*
no locks held by swapper/0/0.
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.18.0-rc3.x86_64 #159
Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090006 05/23/2012
ffffffff8266ac90 ffff880107403af8 ffffffff816db3ef 0000000000000000
ffffffff81c134c0 ffff880107403b58 ffffffff816d6fd3 0000000000000001
ffffffff00000001 ffff880100000000 ffffffff81010e6f 0000000000000046
Call Trace:
<IRQ> [<ffffffff816db3ef>] dump_stack+0x4e/0x68
[<ffffffff816d6fd3>] print_usage_bug+0x1f3/0x204
[<ffffffff81010e6f>] ? save_stack_trace+0x2f/0x50
[<ffffffff810b6f40>] ? print_irq_inversion_bug+0x200/0x200
[<ffffffff810b78e6>] mark_lock+0x176/0x2e0
[<ffffffff810b9f83>] __lock_acquire+0x7c3/0x1c60
[<ffffffff8103d548>] ? lookup_address+0x28/0x30
[<ffffffff8103d58b>] ? _lookup_address_cpa.isra.3+0x3b/0x40
[<ffffffff813c4e89>] ? __debug_check_no_obj_freed+0x89/0x220
[<ffffffff810bbcdc>] lock_acquire+0xfc/0x150
[<ffffffff811ff39c>] ? nr_blockdev_pages+0x1c/0x80
[<ffffffff816e4019>] _raw_spin_lock+0x39/0x50
[<ffffffff811ff39c>] ? nr_blockdev_pages+0x1c/0x80
[<ffffffff811ff39c>] nr_blockdev_pages+0x1c/0x80
[<ffffffff8115d5f7>] si_meminfo+0x47/0x70
[<ffffffff815eb14d>] post_status.isra.3+0x6d/0x190
[<ffffffff810b7f4d>] ? trace_hardirqs_on+0xd/0x10
[<ffffffff8115f00f>] ? __free_pages+0x2f/0x60
[<ffffffff815eb34f>] ? free_balloon_pages.isra.5+0x8f/0xb0
[<ffffffff815eb972>] balloon_onchannelcallback+0x212/0x380
[<ffffffff815e69d3>] vmbus_on_event+0x173/0x1d0
[<ffffffff81071b47>] tasklet_action+0x127/0x160
[<ffffffff81071ffa>] __do_softirq+0x18a/0x340
[<ffffffff81072478>] irq_exit+0x58/0xc0
[<ffffffff810290c5>] hyperv_vector_handler+0x45/0x60
[<ffffffff816e6b92>] hyperv_callback_vector+0x72/0x80
<EOI> [<ffffffff81037b76>] ? native_safe_halt+0x6/0x10
[<ffffffff810b7f4d>] ? trace_hardirqs_on+0xd/0x10
[<ffffffff8100c8d1>] default_idle+0x51/0xf0
[<ffffffff8100d30f>] arch_cpu_idle+0xf/0x20
[<ffffffff810b01e7>] cpu_startup_entry+0x217/0x3f0
[<ffffffff816ce099>] rest_init+0xc9/0xd0
[<ffffffff816cdfd5>] ? rest_init+0x5/0xd0
[<ffffffff81d3d04a>] start_kernel+0x438/0x445
[<ffffffff81d3c94a>] ? set_init_arg+0x57/0x57
[<ffffffff81d3c120>] ? early_idt_handlers+0x120/0x120
[<ffffffff81d3c59f>] x86_64_start_reservations+0x2a/0x2c
[<ffffffff81d3c6df>] x86_64_start_kernel+0x13e/0x14d
Any help deciphering the above is greatly appreciated!
--
Sitsofe | http://sucs.org/~sits/
On Sat, Nov 08, 2014 at 02:36:54PM +0000, Sitsofe Wheeler wrote:
> I've been trying to use the Hyper-V balloon driver to allow the host to
> reclaim unused memory but have been hitting issues. With a Hyper-V 2012
> R2 guest with 4GBytes of RAM, dynamic memory on, 1GByte minimum 10GByte
> maximum, 8 vcpus, running a 3.18.0-rc3 kernel with no swap configured
> the following lockdep splat occurred:
>
> =================================
> [ INFO: inconsistent lock state ]
> 3.18.0-rc3.x86_64 #159 Not tainted
> ---------------------------------
> inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> swapper/0/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
> (bdev_lock){+.?...}, at: [<ffffffff811ff39c>] nr_blockdev_pages+0x1c/0x80
> {SOFTIRQ-ON-W} state was registered at:
> [<ffffffff810ba03d>] __lock_acquire+0x87d/0x1c60
> [<ffffffff810bbcdc>] lock_acquire+0xfc/0x150
> [<ffffffff816e4019>] _raw_spin_lock+0x39/0x50
> [<ffffffff811ff39c>] nr_blockdev_pages+0x1c/0x80
> [<ffffffff8115d5f7>] si_meminfo+0x47/0x70
> [<ffffffff81d6622f>] eventpoll_init+0x11/0x10a
> [<ffffffff81d3d150>] do_one_initcall+0xf9/0x1a7
> [<ffffffff81d3d3d2>] kernel_init_freeable+0x1d4/0x268
> [<ffffffff816ce0ae>] kernel_init+0xe/0x100
> [<ffffffff816e4dfc>] ret_from_fork+0x7c/0xb0
> irq event stamp: 2660283708
> hardirqs last enabled at (2660283708): [<ffffffff8115eef5>] free_hot_cold_page+0x175/0x190
> hardirqs last disabled at (2660283707): [<ffffffff8115ee25>] free_hot_cold_page+0xa5/0x190
> softirqs last enabled at (2660132034): [<ffffffff81071e6a>] _local_bh_enable+0x4a/0x50
> softirqs last disabled at (2660132035): [<ffffffff81072478>] irq_exit+0x58/0xc0
>
> might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(bdev_lock);
> <Interrupt>
> lock(bdev_lock);
>
> *
>
> no locks held by swapper/0/0.
>
>
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.18.0-rc3.x86_64 #159
> Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090006 05/23/2012
> ffffffff8266ac90 ffff880107403af8 ffffffff816db3ef 0000000000000000
> ffffffff81c134c0 ffff880107403b58 ffffffff816d6fd3 0000000000000001
> ffffffff00000001 ffff880100000000 ffffffff81010e6f 0000000000000046
> Call Trace:
> <IRQ> [<ffffffff816db3ef>] dump_stack+0x4e/0x68
> [<ffffffff816d6fd3>] print_usage_bug+0x1f3/0x204
> [<ffffffff81010e6f>] ? save_stack_trace+0x2f/0x50
> [<ffffffff810b6f40>] ? print_irq_inversion_bug+0x200/0x200
> [<ffffffff810b78e6>] mark_lock+0x176/0x2e0
> [<ffffffff810b9f83>] __lock_acquire+0x7c3/0x1c60
> [<ffffffff8103d548>] ? lookup_address+0x28/0x30
> [<ffffffff8103d58b>] ? _lookup_address_cpa.isra.3+0x3b/0x40
> [<ffffffff813c4e89>] ? __debug_check_no_obj_freed+0x89/0x220
> [<ffffffff810bbcdc>] lock_acquire+0xfc/0x150
> [<ffffffff811ff39c>] ? nr_blockdev_pages+0x1c/0x80
> [<ffffffff816e4019>] _raw_spin_lock+0x39/0x50
> [<ffffffff811ff39c>] ? nr_blockdev_pages+0x1c/0x80
> [<ffffffff811ff39c>] nr_blockdev_pages+0x1c/0x80
> [<ffffffff8115d5f7>] si_meminfo+0x47/0x70
> [<ffffffff815eb14d>] post_status.isra.3+0x6d/0x190
> [<ffffffff810b7f4d>] ? trace_hardirqs_on+0xd/0x10
> [<ffffffff8115f00f>] ? __free_pages+0x2f/0x60
> [<ffffffff815eb34f>] ? free_balloon_pages.isra.5+0x8f/0xb0
> [<ffffffff815eb972>] balloon_onchannelcallback+0x212/0x380
> [<ffffffff815e69d3>] vmbus_on_event+0x173/0x1d0
> [<ffffffff81071b47>] tasklet_action+0x127/0x160
> [<ffffffff81071ffa>] __do_softirq+0x18a/0x340
> [<ffffffff81072478>] irq_exit+0x58/0xc0
> [<ffffffff810290c5>] hyperv_vector_handler+0x45/0x60
> [<ffffffff816e6b92>] hyperv_callback_vector+0x72/0x80
> <EOI> [<ffffffff81037b76>] ? native_safe_halt+0x6/0x10
> [<ffffffff810b7f4d>] ? trace_hardirqs_on+0xd/0x10
> [<ffffffff8100c8d1>] default_idle+0x51/0xf0
> [<ffffffff8100d30f>] arch_cpu_idle+0xf/0x20
> [<ffffffff810b01e7>] cpu_startup_entry+0x217/0x3f0
> [<ffffffff816ce099>] rest_init+0xc9/0xd0
> [<ffffffff816cdfd5>] ? rest_init+0x5/0xd0
> [<ffffffff81d3d04a>] start_kernel+0x438/0x445
> [<ffffffff81d3c94a>] ? set_init_arg+0x57/0x57
> [<ffffffff81d3c120>] ? early_idt_handlers+0x120/0x120
> [<ffffffff81d3c59f>] x86_64_start_reservations+0x2a/0x2c
> [<ffffffff81d3c6df>] x86_64_start_kernel+0x13e/0x14d
>
> Any help deciphering the above is greatly appreciated!
Its fairly simple, the first trace shows where bdev_lock was taken with
softirqs enabled, and the second trace shows where its taken from
softirqs. Combine the two and you've got a recursive deadlock.
I don't know the block layer very well, but a quick glance at the code
shows its bdev_lock isn't meant to be used from softirq context,
therefore the hyperv stuff is broken.
So complain to the hyperv people.
> -----Original Message-----
> From: Peter Zijlstra [mailto:[email protected]]
> Sent: Monday, November 10, 2014 1:44 AM
> To: Sitsofe Wheeler
> Cc: KY Srinivasan; Haiyang Zhang; [email protected]; Ingo Molnar;
> [email protected]
> Subject: Re: Inconsistent lock state with Hyper-V memory balloon?
>
> On Sat, Nov 08, 2014 at 02:36:54PM +0000, Sitsofe Wheeler wrote:
> > I've been trying to use the Hyper-V balloon driver to allow the host
> > to reclaim unused memory but have been hitting issues. With a Hyper-V
> > 2012
> > R2 guest with 4GBytes of RAM, dynamic memory on, 1GByte minimum
> > 10GByte maximum, 8 vcpus, running a 3.18.0-rc3 kernel with no swap
> > configured the following lockdep splat occurred:
> >
> > =================================
> > [ INFO: inconsistent lock state ]
> > 3.18.0-rc3.x86_64 #159 Not tainted
> > ---------------------------------
> > inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> > swapper/0/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
> > (bdev_lock){+.?...}, at: [<ffffffff811ff39c>]
> > nr_blockdev_pages+0x1c/0x80 {SOFTIRQ-ON-W} state was registered at:
> > [<ffffffff810ba03d>] __lock_acquire+0x87d/0x1c60
> > [<ffffffff810bbcdc>] lock_acquire+0xfc/0x150
> > [<ffffffff816e4019>] _raw_spin_lock+0x39/0x50
> > [<ffffffff811ff39c>] nr_blockdev_pages+0x1c/0x80
> > [<ffffffff8115d5f7>] si_meminfo+0x47/0x70
> > [<ffffffff81d6622f>] eventpoll_init+0x11/0x10a
> > [<ffffffff81d3d150>] do_one_initcall+0xf9/0x1a7
> > [<ffffffff81d3d3d2>] kernel_init_freeable+0x1d4/0x268
> > [<ffffffff816ce0ae>] kernel_init+0xe/0x100
> > [<ffffffff816e4dfc>] ret_from_fork+0x7c/0xb0 irq event stamp:
> > 2660283708 hardirqs last enabled at (2660283708):
> > [<ffffffff8115eef5>] free_hot_cold_page+0x175/0x190 hardirqs last
> > disabled at (2660283707): [<ffffffff8115ee25>]
> > free_hot_cold_page+0xa5/0x190 softirqs last enabled at (2660132034):
> > [<ffffffff81071e6a>] _local_bh_enable+0x4a/0x50 softirqs last disabled
> > at (2660132035): [<ffffffff81072478>] irq_exit+0x58/0xc0
> >
> > might help us debug this:
> > Possible unsafe locking scenario:
> >
> > CPU0
> > ----
> > lock(bdev_lock);
> > <Interrupt>
> > lock(bdev_lock);
> >
> > *
> >
> > no locks held by swapper/0/0.
> >
> >
> > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.18.0-rc3.x86_64 #159
> > Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine,
> > BIOS 090006 05/23/2012
> > ffffffff8266ac90 ffff880107403af8 ffffffff816db3ef 0000000000000000
> > ffffffff81c134c0 ffff880107403b58 ffffffff816d6fd3 0000000000000001
> > ffffffff00000001 ffff880100000000 ffffffff81010e6f 0000000000000046
> > Call Trace:
> > <IRQ> [<ffffffff816db3ef>] dump_stack+0x4e/0x68
> > [<ffffffff816d6fd3>] print_usage_bug+0x1f3/0x204 [<ffffffff81010e6f>]
> > ? save_stack_trace+0x2f/0x50 [<ffffffff810b6f40>] ?
> > print_irq_inversion_bug+0x200/0x200
> > [<ffffffff810b78e6>] mark_lock+0x176/0x2e0 [<ffffffff810b9f83>]
> > __lock_acquire+0x7c3/0x1c60 [<ffffffff8103d548>] ?
> > lookup_address+0x28/0x30 [<ffffffff8103d58b>] ?
> > _lookup_address_cpa.isra.3+0x3b/0x40
> > [<ffffffff813c4e89>] ? __debug_check_no_obj_freed+0x89/0x220
> > [<ffffffff810bbcdc>] lock_acquire+0xfc/0x150 [<ffffffff811ff39c>] ?
> > nr_blockdev_pages+0x1c/0x80 [<ffffffff816e4019>]
> > _raw_spin_lock+0x39/0x50 [<ffffffff811ff39c>] ?
> > nr_blockdev_pages+0x1c/0x80 [<ffffffff811ff39c>]
> > nr_blockdev_pages+0x1c/0x80 [<ffffffff8115d5f7>]
> si_meminfo+0x47/0x70
> > [<ffffffff815eb14d>] post_status.isra.3+0x6d/0x190
> > [<ffffffff810b7f4d>] ? trace_hardirqs_on+0xd/0x10
> > [<ffffffff8115f00f>] ? __free_pages+0x2f/0x60 [<ffffffff815eb34f>] ?
> > free_balloon_pages.isra.5+0x8f/0xb0
> > [<ffffffff815eb972>] balloon_onchannelcallback+0x212/0x380
> > [<ffffffff815e69d3>] vmbus_on_event+0x173/0x1d0 [<ffffffff81071b47>]
> > tasklet_action+0x127/0x160 [<ffffffff81071ffa>]
> > __do_softirq+0x18a/0x340 [<ffffffff81072478>] irq_exit+0x58/0xc0
> > [<ffffffff810290c5>] hyperv_vector_handler+0x45/0x60
> > [<ffffffff816e6b92>] hyperv_callback_vector+0x72/0x80 <EOI>
> > [<ffffffff81037b76>] ? native_safe_halt+0x6/0x10 [<ffffffff810b7f4d>]
> > ? trace_hardirqs_on+0xd/0x10 [<ffffffff8100c8d1>]
> > default_idle+0x51/0xf0 [<ffffffff8100d30f>] arch_cpu_idle+0xf/0x20
> > [<ffffffff810b01e7>] cpu_startup_entry+0x217/0x3f0
> > [<ffffffff816ce099>] rest_init+0xc9/0xd0 [<ffffffff816cdfd5>] ?
> > rest_init+0x5/0xd0 [<ffffffff81d3d04a>] start_kernel+0x438/0x445
> > [<ffffffff81d3c94a>] ? set_init_arg+0x57/0x57 [<ffffffff81d3c120>] ?
> > early_idt_handlers+0x120/0x120 [<ffffffff81d3c59f>]
> > x86_64_start_reservations+0x2a/0x2c
> > [<ffffffff81d3c6df>] x86_64_start_kernel+0x13e/0x14d
> >
> > Any help deciphering the above is greatly appreciated!
>
> Its fairly simple, the first trace shows where bdev_lock was taken with
> softirqs enabled, and the second trace shows where its taken from softirqs.
> Combine the two and you've got a recursive deadlock.
>
> I don't know the block layer very well, but a quick glance at the code shows
> its bdev_lock isn't meant to be used from softirq context, therefore the
> hyperv stuff is broken.
>
> So complain to the hyperv people.
Sitsofe,
I am on vacation in India till the the 17th of November. I will look at this and fix this issue when I get back.
Regards,
K. Y
Sitsofe, can you try the patch attached to see if it helps with the problem?
Long
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Peter Zijlstra
Sent: Monday, November 10, 2014 1:44 AM
To: Sitsofe Wheeler
Cc: KY Srinivasan; Haiyang Zhang; [email protected]; Ingo Molnar; [email protected]
Subject: Re: Inconsistent lock state with Hyper-V memory balloon?
On Sat, Nov 08, 2014 at 02:36:54PM +0000, Sitsofe Wheeler wrote:
> I've been trying to use the Hyper-V balloon driver to allow the host
> to reclaim unused memory but have been hitting issues. With a Hyper-V
> 2012
> R2 guest with 4GBytes of RAM, dynamic memory on, 1GByte minimum
> 10GByte maximum, 8 vcpus, running a 3.18.0-rc3 kernel with no swap
> configured the following lockdep splat occurred:
>
> =================================
> [ INFO: inconsistent lock state ]
> 3.18.0-rc3.x86_64 #159 Not tainted
> ---------------------------------
> inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> swapper/0/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
> (bdev_lock){+.?...}, at: [<ffffffff811ff39c>]
> nr_blockdev_pages+0x1c/0x80 {SOFTIRQ-ON-W} state was registered at:
> [<ffffffff810ba03d>] __lock_acquire+0x87d/0x1c60
> [<ffffffff810bbcdc>] lock_acquire+0xfc/0x150
> [<ffffffff816e4019>] _raw_spin_lock+0x39/0x50
> [<ffffffff811ff39c>] nr_blockdev_pages+0x1c/0x80
> [<ffffffff8115d5f7>] si_meminfo+0x47/0x70
> [<ffffffff81d6622f>] eventpoll_init+0x11/0x10a
> [<ffffffff81d3d150>] do_one_initcall+0xf9/0x1a7
> [<ffffffff81d3d3d2>] kernel_init_freeable+0x1d4/0x268
> [<ffffffff816ce0ae>] kernel_init+0xe/0x100
> [<ffffffff816e4dfc>] ret_from_fork+0x7c/0xb0 irq event stamp:
> 2660283708 hardirqs last enabled at (2660283708):
> [<ffffffff8115eef5>] free_hot_cold_page+0x175/0x190 hardirqs last
> disabled at (2660283707): [<ffffffff8115ee25>]
> free_hot_cold_page+0xa5/0x190 softirqs last enabled at (2660132034):
> [<ffffffff81071e6a>] _local_bh_enable+0x4a/0x50 softirqs last disabled
> at (2660132035): [<ffffffff81072478>] irq_exit+0x58/0xc0
>
> might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(bdev_lock);
> <Interrupt>
> lock(bdev_lock);
>
> *
>
> no locks held by swapper/0/0.
>
>
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.18.0-rc3.x86_64 #159
> Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine,
> BIOS 090006 05/23/2012
> ffffffff8266ac90 ffff880107403af8 ffffffff816db3ef 0000000000000000
> ffffffff81c134c0 ffff880107403b58 ffffffff816d6fd3 0000000000000001
> ffffffff00000001 ffff880100000000 ffffffff81010e6f 0000000000000046
> Call Trace:
> <IRQ> [<ffffffff816db3ef>] dump_stack+0x4e/0x68
> [<ffffffff816d6fd3>] print_usage_bug+0x1f3/0x204 [<ffffffff81010e6f>]
> ? save_stack_trace+0x2f/0x50 [<ffffffff810b6f40>] ?
> print_irq_inversion_bug+0x200/0x200
> [<ffffffff810b78e6>] mark_lock+0x176/0x2e0 [<ffffffff810b9f83>]
> __lock_acquire+0x7c3/0x1c60 [<ffffffff8103d548>] ?
> lookup_address+0x28/0x30 [<ffffffff8103d58b>] ?
> _lookup_address_cpa.isra.3+0x3b/0x40
> [<ffffffff813c4e89>] ? __debug_check_no_obj_freed+0x89/0x220
> [<ffffffff810bbcdc>] lock_acquire+0xfc/0x150 [<ffffffff811ff39c>] ?
> nr_blockdev_pages+0x1c/0x80 [<ffffffff816e4019>]
> _raw_spin_lock+0x39/0x50 [<ffffffff811ff39c>] ?
> nr_blockdev_pages+0x1c/0x80 [<ffffffff811ff39c>]
> nr_blockdev_pages+0x1c/0x80 [<ffffffff8115d5f7>] si_meminfo+0x47/0x70
> [<ffffffff815eb14d>] post_status.isra.3+0x6d/0x190
> [<ffffffff810b7f4d>] ? trace_hardirqs_on+0xd/0x10
> [<ffffffff8115f00f>] ? __free_pages+0x2f/0x60 [<ffffffff815eb34f>] ?
> free_balloon_pages.isra.5+0x8f/0xb0
> [<ffffffff815eb972>] balloon_onchannelcallback+0x212/0x380
> [<ffffffff815e69d3>] vmbus_on_event+0x173/0x1d0 [<ffffffff81071b47>]
> tasklet_action+0x127/0x160 [<ffffffff81071ffa>]
> __do_softirq+0x18a/0x340 [<ffffffff81072478>] irq_exit+0x58/0xc0
> [<ffffffff810290c5>] hyperv_vector_handler+0x45/0x60
> [<ffffffff816e6b92>] hyperv_callback_vector+0x72/0x80 <EOI>
> [<ffffffff81037b76>] ? native_safe_halt+0x6/0x10 [<ffffffff810b7f4d>]
> ? trace_hardirqs_on+0xd/0x10 [<ffffffff8100c8d1>]
> default_idle+0x51/0xf0 [<ffffffff8100d30f>] arch_cpu_idle+0xf/0x20
> [<ffffffff810b01e7>] cpu_startup_entry+0x217/0x3f0
> [<ffffffff816ce099>] rest_init+0xc9/0xd0 [<ffffffff816cdfd5>] ?
> rest_init+0x5/0xd0 [<ffffffff81d3d04a>] start_kernel+0x438/0x445
> [<ffffffff81d3c94a>] ? set_init_arg+0x57/0x57 [<ffffffff81d3c120>] ?
> early_idt_handlers+0x120/0x120 [<ffffffff81d3c59f>]
> x86_64_start_reservations+0x2a/0x2c
> [<ffffffff81d3c6df>] x86_64_start_kernel+0x13e/0x14d
>
> Any help deciphering the above is greatly appreciated!
Its fairly simple, the first trace shows where bdev_lock was taken with softirqs enabled, and the second trace shows where its taken from softirqs. Combine the two and you've got a recursive deadlock.
I don't know the block layer very well, but a quick glance at the code shows its bdev_lock isn't meant to be used from softirq context, therefore the hyperv stuff is broken.
So complain to the hyperv people.