Re: handle_pio looping during domain shutdown, with qemu 4.2.0 in stubdom

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.06.2020 03:46, Marek Marczykowski-Górecki wrote:
> Hi,
> 
> (continuation of a thread from #xendevel)
> 
> During system shutdown quite often I hit infinite stream of errors like
> this:
> 
>     (XEN) d3v0 Weird PIO status 1, port 0xb004 read 0xffff
>     (XEN) domain_crash called from io.c:178
> 
> This is all running on Xen 4.13.0 (I think I've got this with 4.13.1
> too), nested within KVM. The KVM part means everything is very slow, so
> various race conditions are much more likely to happen.
> 
> It started happening not long ago, and I'm pretty sure it's about
> updating to qemu 4.2.0 (in linux stubdom), previous one was 3.0.0.
> 
> Thanks to Andrew and Roger, I've managed to collect more info.
> 
> Context:
>     dom0: pv
>     dom1: hvm
>     dom2: stubdom for dom1
>     dom3: hvm
>     dom4: stubdom for dom3
>     dom5: pvh
>     dom6: pvh
> 
> It starts I think ok:
> 
>     (XEN) hvm.c:1620:d6v0 All CPUs offline -- powering off.
>     (XEN) d3v0 handle_pio port 0xb004 read 0x0000
>     (XEN) d3v0 handle_pio port 0xb004 read 0x0000
>     (XEN) d3v0 handle_pio port 0xb004 write 0x0001
>     (XEN) d3v0 handle_pio port 0xb004 write 0x2001
>     (XEN) d4v0 XEN_DMOP_remote_shutdown domain 3 reason 0

I can't seem to be able to spot the call site of this, in any of
qemu, libxl, or libxc. I'm in particular curious as to the further
actions taken on the domain after this was invoked: Do any ioreq
servers get unregistered immediately (which I think would be a
problem)?

Jan