>> I'm using both of them applied on top of 2.0 in production and have no
>> problems with them. I'm using NFS exclusively with cache=none.
>>
>> So, I shall test vm-migration and drive-migration with 2.1.0-rc2 with no
>> extra patches applied or reverted, on VM that is running fio, am I correct?
>>
>
> Yes, exactly. ISCSI-based setup can take some minutes to deploy, given
> prepared image, and I have one hundred percent hit rate for the
> original issue with it.

I've reproduced your IO hang with 2.0 and both 
9b1786829aefb83f37a8f3135e3ea91c56001b56 and 
a096b3a6732f846ec57dc28b47ee9435aa0609bf applied.

Reverting 9b1786829aefb83f37a8f3135e3ea91c56001b56 indeed fixes the 
problem (but reintroduces block-migration hang). It's seems like qemu 
bug rather than guest problem, as no-kvmclock parameters makes no 
difference. IO just stops, all qemu IO threads die off. Almost like it 
forgets to migrate them:-)

I'm attaching backtrace from guest kernel and qemu and qemu command line.

Going to compile 2.1-rc.

-- 
mg