linux-kernel - Re: [PATCH v2 00/18] Entry stack switching

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Date:   Wed, 22 Nov 2017 08:23:20 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v2 00/18] Entry stack switching

On Tue, Nov 21, 2017 at 10:22 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Andy Lutomirski <luto@...nel.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?