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

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Date:   Thu, 23 Nov 2017 17:41:58 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
cc:     Ingo Molnar <mingo@...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 Thu, 23 Nov 2017, Andy Lutomirski wrote:
> On Wed, Nov 22, 2017 at 10:58 PM, Ingo Molnar <mingo@...nel.org> wrote:
> > * Ingo Molnar <mingo@...nel.org> wrote:
> >> * Ingo Molnar <mingo@...nel.org> wrote:
> >>
> >> > > 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?
> >> >
> >> > Ok, it should be bisectable, will try to bisect it.
> >>
> >> The latestest entry-stack code appears to be working fine though.
> >>
> >> So one of the below fixes from yesterday appears to have done the trick.
> >>
> >> I'll re-test today to make sure: maybe it's more sporadic than I thought, in one
> >> of the bootups I got the do_IRQ warning only once, in half a day of uptime.
> >
> > I re-tested and it all seems fine now. I suspect it got fixed by:
> >
> >   ca37e57bbe0c: x86/entry/64: Add missing irqflags tracing to native_load_gs_index()
> >
> > still it is weird, because I boot that system with latest -tip on a daily basis,
> > and don't remember having seen that warning.
> >
> > Do you have any theory for why the entry stack changes would uncover this bug?
> 
> No.  I also don't see why it would have anything to do with irqflag
> tracing.  As far as I know, the unhandled IRQ warning has nothing to
> do with tracing or lockdep.

I suspect its more likely some subtle interaction with that newfangled
vector management code. You should poke the grumpy old greybeard.

Thanks,

	tglx