Re: [Xen-devel] Xen-unstable: pci-passthrough "irq 16: nobody cared" on HVM guest shutdown on irq of device not passed through.

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Friday, September 26, 2014, 11:43:04 AM, you wrote:

>>>> On 26.09.14 at 11:18, <linux@xxxxxxxxxxxxxx> wrote:
>> Friday, September 26, 2014, 8:59:22 AM, you wrote:
>>>>>> On 26.09.14 at 00:09, <linux@xxxxxxxxxxxxxx> wrote:
>>>> - Tried switching off the onboard soundcard in the bios. Now irq16 is not 
>>>> bound 
>>>>   to any device, but the machine still freezes without any error (on 
>>>> serial 
>>>>   console with sync-console on, triple ctrl-a also doesn't work anymore)
>> 
>>> I suppose that hang is with irqpoll still in use? Ctrl-a not working anymore
>>> makes me wonder whether you use a PCI serial card sitting on that same
>>> IRQ for the Xen console... 
>> 
>> With and without irqpoll in use. 

> Oh, even without. That's worrying indeed. But again, the main thing
> to understand is who sets up and unmasks IRQ 16 when and for
> what reason.

After i disabled the sound device in the bios, irq16 is not setup anymore.
It's not present in /proc/interrupts, i don't see it in the logs (no gsi 16, 
no irq 16)
I also don't get the "irq 16 nobody cared" anymore, but instead a freeze.

So i'm a bit inclined to say that it is a coincidence that what ever is wrong 
always seems to hit that when it was present, but is hitting something else 
less 
verbose now and freezing the machine.

>> I don't know what happens if there is a race / ordering problem in say 
>> xen/iommu/pciback pulling 
>> the device from the guest on shutdown while there are still irq's pending ?
>> 
>> (the code of xen_pciback's release and resetting function for instance seems 
>> to do a different 
>> ordering compared to vfio-pci's)

> That's a different aspect, as long as I recall correctly that the passed
> through device isn't itself sitting on IRQ 16.

No it's not, but i don't know what would happen if the devices is being reset 
before being completely disabled / have irq's disabled. And it issues an irq 
request, for an irq that isn't handled/registered anymore, but i would assume 
it to 
be discarded and an error message printed .. 

The other strange thing is that i don't have problems with restarting HVM 
guests 
with other passed through device types (usb controllers, videograbber), only 
difference regarding irq's is that they use intx of msi-x and not msi.

>>> Furthermore in that mode (with supposedly no
>>> handler set up for IRQ 16) monitoring (with a little bit of debugging code)
>>> how/when IRQ 16 gets setup and unmasked may provide further hints.
>> 
>> I don't know if i made it clear enough, but without the device occupying 
>> irq16 
>> it doesn't give the irq16 nobody cared (or any such message or error), it 
>> just 
>> freezes.

> Because likely it doesn't even get that far.

> Jan




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