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Date:	Mon, 10 Nov 2014 09:47:06 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Sitsofe Wheeler <sitsofe@...il.com>
CC:	Haiyang Zhang <haiyangz@...rosoft.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: Inconsistent lock state with Hyper-V memory balloon?



> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Monday, November 10, 2014 1:44 AM
> To: Sitsofe Wheeler
> Cc: KY Srinivasan; Haiyang Zhang; devel@...uxdriverproject.org; Ingo Molnar;
> linux-kernel@...r.kernel.org
> 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
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