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

[Marcin Gibuła]

> > 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

io-hang.patch
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