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

["Marcin Gibuła" <m.gibula@beyond.pl>]

>> 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.

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.

-- 
mg