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SubjectRe: [PATCH v2 00/18] Entry stack switching
On Tue, Nov 21, 2017 at 10:22 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Andy Lutomirski <luto@kernel.org> wrote:
>
>> This sets up stack switching, including for SYSCALL. I think it's
>> in decent shape.
>>
>> Known issues:
>> - I think we're going to want a way to turn the stack switching on and
>> off either at boot time or at runtime. It should be fairly straightforward
>> to make it work.
>>
>> - I think the ORC unwinder isn't so good at dealing with stack overflows.
>> It bails too early (I think), resulting in lots of ? entries. This
>> isn't a regression with this series -- it's just something that could
>> be improved.
>>
>> Ingo, patch 1 may be tip/urgent material. It fixes what I think is
>> a bug in Xen. I'm having a hard time testing because it's being
>> masked by a bigger unrelated bug that's keeping Xen from booting
>> when configured to hit the bug I'm fixing. (The latter bug goes at
>> least back to v4.13, I think I know roughtly what's wrong, and I've
>> reported it to the maintainers.)
>
> Hm, with this series the previous IRQ vector bug appears again:
>
> [ 51.156370] do_IRQ: 16.34 No irq handler for vector
> [ 57.511030] do_IRQ: 16.34 No irq handler for vector
> [ 57.528335] do_IRQ: 16.34 No irq handler for vector
> [ 57.533256] do_IRQ: 16.34 No irq handler for vector
> [ 63.991913] do_IRQ: 16.34 No irq handler for vector
> [ 63.996810] do_IRQ: 16.34 No irq handler for vector
>
> I've attached the reproducer config. Note that the system appears to be working to
> a certain extent (I could ssh to it and extract its config), but produces these
> warnings sporadically.

I'll try to reproduce this, but this is weird. This is vector 34,
which is, or could be, a genuine IRQ vector. The only way I can think
of that my series would have caused this is if I very severely broke
common_interrupt, but I don't see how that could have happened without
breaking everything. It's also weird that you're seeing this only on
CPU 16. Maybe it's worth adding a WARN_ON to that warning to get a
stack trace just in case.

Thomas, any insight here?

> but don't get the IRQ vector warnings.

Ingo, are you saying that you only get the IRQ vector warnings with
the SYSCALL hwframe fix applied? That's bizarre.

Anyway, I booted your config (more or less -- I munged it through
virtme-configkernel --update first) with 17 vCPUs and it seems fine.
Is the issue reliable enough to bisect?

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