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

[Andrey Korolyov]

On Sun, Jul 13, 2014 at 4:28 PM, Andrey Korolyov <address@hidden> wrote:
> Hello,
>
> the issue is not specific to the iothread code because generic
> virtio-blk also hangs up:
>
> Given code set like in the
> http://www.mail-archive.com/address@hidden/msg246164.html,
> launch a VM with virtio-blk disk and writeback rbd backend, fire up
> fio, migrate once with libvirt:
>
> time virsh migrate vm27842 qemu+tcp://10.6.0.10/system --live
> --persistent --undefinesource --timeout 60
>
>
> real    1m2.969s
> user    0m0.016s
> sys     0m0.008s
>
> For ones who are unfamiliar with libvirt syntax this means that the
> live migration was failed to complete over sixty seconds, VM was
> frozen, moved and re-launched at the destination. After this, I/O gets
> stuck forever. Any diagnostic information is available upon request if
> there will be difficulties repeating the issue.

Small follow-up: issue have probabilistic nature, as it looks - by
limited number of runs, it is reproducible within three cases:
 1) live migration went well, I/O locked up,
 2) live migration failed by timeout, I/O locked up,
 3) live migration went well and disk was not locked, but on backward
migration we are always hitting 2).