Re: Deadlock in stdvga_mem_accept() with emulation

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 13/07/15 09:50, Razvan Cojocaru wrote:
> On 07/13/2015 11:10 AM, Andrew Cooper wrote:
>> On 13/07/2015 08:48, Razvan Cojocaru wrote:
>>> Hello,
>>>
>>> I'm battling the following hypervisor crash with current staging:
>>>
>>> (d2) Invoking ROMBIOS ...
>>> (XEN) stdvga.c:147:d2v0 entering stdvga and caching modes
>>> (d2) VGABios $Id: vgabios.c,v 1.67 2008/01/27 09:44:12 vruppert Exp $
>>> (XEN) Watchdog timer detects that CPU7 is stuck!
>>> (XEN) ----[ Xen-4.6-unstable  x86_64  debug=y  Not tainted ]----
>>> (XEN) CPU:    7
>>> (XEN) RIP:    e008:[<ffff82d08012c3f1>] _spin_lock+0x31/0x54
>>> (XEN) RFLAGS: 0000000000000202   CONTEXT: hypervisor (d2v0)
>>> (XEN) rax: 000000000000c11d   rbx: ffff83041e687970   rcx: 000000000000c11e
>>> (XEN) rdx: ffff83041e687970   rsi: 000000000000c11e   rdi: ffff83041e687978
>>> (XEN) rbp: ffff83040eb37208   rsp: ffff83040eb37200   r8:  0000000000000000
>>> (XEN) r9:  0000000000000000   r10: ffff82d08028c3c0   r11: 0000000000000000
>>> (XEN) r12: ffff83041e687000   r13: ffff83041e687970   r14: ffff83040eb37278
>>> (XEN) r15: 00000000000c253f   cr0: 000000008005003b   cr4: 00000000001526e0
>>> (XEN) cr3: 00000004054a0000   cr2: 0000000000000000
>>> (XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: 0000   cs: e008
>>> (XEN) Xen stack trace from rsp=ffff83040eb37200:
>>> (XEN)    ffff83040eb37278 ffff83040eb37238 ffff82d0801d09b6 0000000000000282
>>> (XEN)    0000000000000008 ffff830403791bf0 ffff83041e687000 ffff83040eb37268
>>> (XEN)    ffff82d0801cb23a 00000000000c253f ffff8300d85fc000 0000000000000001
>>> (XEN)    00000000000000c2 ffff83040eb37298 ffff82d0801cb410 00000000000c253f
>>> (XEN)    0000000000000000 0000000100000001 0100000000000000 ffff83040eb37328
>>> (XEN)    ffff82d0801c2403 ffff83040eb37394 ffff83040eb30000 0000000000000000
>>> (XEN)    ffff83040eb37360 00000000000000c2 ffff8304054cb000 000000000000053f
>>> (XEN)    0000000000000002 0000000000000000 ffff83040eb373f4 00000000000000c2
>>> (XEN)    ffff83040eb373d8 0000000000000000 0000000000000000 ffff82d08028c620
>>> (XEN)    0000000000000000 ffff83040eb37338 ffff82d0801c3e5d ffff83040eb37398
>>> (XEN)    ffff82d0801cb107 000000010eb37394 ffff830403791bf0 ffff830403791bf0
>>> (XEN)    ffff83041e687000 ffff83040eb37398 ffff830403791bf0 0000000000000001
>>> (XEN)    ffff83040eb373d8 0000000000000001 00000000000c253f ffff83040eb373c8
>>> (XEN)    ffff82d0801cb291 ffff83040eb37b30 ffff8300d85fc000 0000000000000001
>>> (XEN)    0000000000000000 ffff83040eb37428 ffff82d0801bb440 00000000000a0001
>>> (XEN)    00000000000c253f 0000000100000001 0111000000000000 ffff83040eb37478
>>> (XEN)    0000000000000001 0000000000000000 0000000000000000 0000000000000001
>>> (XEN)    0000000000000001 ffff83040eb374a8 ffff82d0801bc0b9 0000000000000001
>>> (XEN)    00000000000c253f ffff8300d85fc000 00000000000a0001 0100000000000000
>>> (XEN)    ffff83040eb37728 ffff82e00819dc60 0000000000000000 ffff83040eb374c8
>>> (XEN) Xen call trace:
>>> (XEN)    [<ffff82d08012c3f1>] _spin_lock+0x31/0x54
>>> (XEN)    [<ffff82d0801d09b6>] stdvga_mem_accept+0x3b/0x125
>>> (XEN)    [<ffff82d0801cb23a>] hvm_find_io_handler+0x68/0x8a
>>> (XEN)    [<ffff82d0801cb410>] hvm_mmio_internal+0x37/0x67
>>> (XEN)    [<ffff82d0801c2403>] __hvm_copy+0xe9/0x37d
>>> (XEN)    [<ffff82d0801c3e5d>] hvm_copy_from_guest_phys+0x14/0x16
>>> (XEN)    [<ffff82d0801cb107>] hvm_process_io_intercept+0x10b/0x1d6
>>> (XEN)    [<ffff82d0801cb291>] hvm_io_intercept+0x35/0x5b
>>> (XEN)    [<ffff82d0801bb440>] hvmemul_do_io+0x1ff/0x2c1
>>> (XEN)    [<ffff82d0801bc0b9>] hvmemul_do_io_addr+0x117/0x163
>>> (XEN)    [<ffff82d0801bc129>] hvmemul_do_mmio_addr+0x24/0x26
>>> (XEN)    [<ffff82d0801bcbb5>] hvmemul_rep_movs+0x1ef/0x335
>>> (XEN)    [<ffff82d080198b49>] x86_emulate+0x56c9/0x13088
>>> (XEN)    [<ffff82d0801bbd26>] _hvm_emulate_one+0x186/0x281
>>> (XEN)    [<ffff82d0801bc1e8>] hvm_emulate_one+0x10/0x12
>>> (XEN)    [<ffff82d0801cb63e>] handle_mmio+0x54/0xd2
>>> (XEN)    [<ffff82d0801cb700>] handle_mmio_with_translation+0x44/0x46
>>> (XEN)    [<ffff82d0801c27f6>] hvm_hap_nested_page_fault+0x15f/0x589
>>> (XEN)    [<ffff82d0801e9741>] vmx_vmexit_handler+0x150e/0x188d
>>> (XEN)    [<ffff82d0801ee7d1>] vmx_asm_vmexit_handler+0x41/0xc0
>>> (XEN)
>>> (XEN)
>>> (XEN) ****************************************
>>> (XEN) Panic on CPU 7:
>>> (XEN) FATAL TRAP: vector = 2 (nmi)
>>> (XEN) [error_code=0000]
>>> (XEN) ****************************************
>>>
>>> At first I thought it was caused by V5 of the vm_event-based
>>> introspection series, but I've rolled it back enough to apply V4 on top
>>> of it (which has been thoroughly tested on Thursday), and it still
>>> happens, so this would at least appear to be unrelated at this point
>>> (other than the fact that our use case is maybe somewhat unusual with
>>> heavy emulation).
>>>
>>> I'll keep digging, but since this is a busy time for Xen I thought I'd
>>> issue a heads-up here as soon as possible, in case the problem is
>>> obvious for somebody and it helps getting it fixed sooner.
>> In c/s 3bbaaec09b1b942f5624dee176da6e416d31f982 there is now a
>> deliberate split between stdvga_mem_accept() and stdvga_mem_complete()
>> about locking and unlocking the stdvga lock.
>>
>> At a guess, the previous chain of execution accidentally omitted the
>> stdvga_mem_complete() call.
> Thanks, I've reverted that patch and the crash is gone. I'll be happy to
> test a fix if one is provided, but I don't know enough about that code
> to go mess with it...

Thanks - that is a useful datapoint.

What exactly are you attempting to boot in this VM?

~Andrew