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Re: [Qemu-devel] Assertion failure taking external snapshot with virtio


From: Ed Swierk
Subject: Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread
Date: Fri, 17 Mar 2017 10:32:47 -0700

On Fri, Mar 17, 2017 at 10:15 AM, Paolo Bonzini <address@hidden> wrote:
>
>
> On 17/03/2017 18:11, Paolo Bonzini wrote:
>>
>>
>> On 17/03/2017 17:55, Ed Swierk wrote:
>>> I'm running into the same problem taking an external snapshot with a
>>> virtio-blk drive with iothread, so it's not specific to virtio-scsi.
>>> Run a Linux guest on qemu master
>>>
>>>   qemu-system-x86_64 -nographic -enable-kvm -monitor
>>> telnet:0.0.0.0:1234,server,nowait -m 1024 -object
>>> iothread,id=iothread1 -drive file=/x/drive.qcow2,if=none,id=drive0
>>> -device virtio-blk-pci,iothread=iothread1,drive=drive0
>>>
>>> Then in the monitor
>>>
>>>   snapshot_blkdev drive0 /x/snap1.qcow2
>>>
>>> qemu bombs with
>>>
>>>   qemu-system-x86_64: /x/qemu/include/block/aio.h:457:
>>> aio_enable_external: Assertion `ctx->external_disable_cnt > 0' failed.
>>>
>>> whereas without the iothread the assertion failure does not occur.
>>
>> Please try this patch:
>
> Hmm, no.  I'll post the full fix on top of John Snow's patches.

OK. Incidentally, testing with virtio-blk I bisected the assertion
failure to b2c2832c6140cfe3ddc0de2d77eeb0b77dea8fd3 ("block: Add Error
parameter to bdrv_append()").

--Ed



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