Re: [Qemu-devel] latest rc: virtio-blk hangs forever after migration

[Andrey Korolyov]

On Thu, Jul 17, 2014 at 5:25 PM, Marcin Gibuła <address@hidden> wrote:
>>> 2.1-rc2 behaves exactly the same.
>>>
>>> Interestingly enough, reseting guest system causes I/O to work again. So
>>> it's not qemu that hangs on IO, rather it fails to notify guest about
>>> completed operations that were issued during migration.
>>>
>>> And its somehow caused by calling cpu_synchronize_all_states() inside
>>> kvmclock_vm_state_change().
>>>
>>>
>>>
>>> As for testing with cache=writeback, I'll try to setup some iscsi to test
>>> it.
>>
>>
>> Awesome, thanks! AFAIK you`ll not be able to use write cache with
>> iscsi for migration. VM which had a reset before hangs always when
>> freshly launched have a chance to be migrated successfully. And yes,
>> it looks like lower layer forgetting to notify driver about some
>> operations at a glance.
>
>
> Andrey,
>
> could you try attached patch? It's an incredibly ugly workaround that calls
> cpu_synchronize_all_states() in a way that bypasses lazy execution logic.
>
> But it works for me. If that works for you as well, its somehow related to
> lazy execution of cpu_synchronize_all_states.
>
> --
> mg

Yes, it working well with writeback cache too.