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Subject: Re: [Qemu-devel] latest rc: virtio-blk hangs forever after migration
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To: Andrey Korolyov <andrey@xdel.ru>
Cc: Amit Shah <amit.shah@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, Fam Zheng <famz@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

> 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:-)

Some more info:

a) 2.0 + 9b1786829aefb83f37a8f3135e3ea91c56001b56 + 
a096b3a6732f846ec57dc28b47ee9435aa0609bf = hangs

b) 2.0 + 9b1786829aefb83f37a8f3135e3ea91c56001b56 = works

c) 2.0 + 9b1786829aefb83f37a8f3135e3ea91c56001b56 + move 
cpu_synchronize_state to migration.c = works

Tested with NFS (qcow2) + cache=none.

IO is dead only for disk that was being written to during migration.
I.e. if my test VM has two disks: vda and vdb, and I'm running fio on 
vdb and it hangs after migration, I can still issue writes to vda.

Recreation steps:
1. Create VM
2. Run fio (Andrey's config)
3. Live migrate VM couple of times.

-- 
mg