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SubjectRe: [PATCH 3/3] x86/mm, tracing: Fix CR2 corruption
On Wed, Jul 3, 2019 at 3:01 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Wed, Jul 03, 2019 at 01:27:09PM -0700, Andy Lutomirski wrote:
> > On Wed, Jul 3, 2019 at 3:28 AM root <peterz@infradead.org> wrote:
>
> > > @@ -1338,18 +1347,9 @@ ENTRY(error_entry)
> > > movq %rax, %rsp /* switch stack */
> > > ENCODE_FRAME_POINTER
> > > pushq %r12
> > > -
> > > - /*
> > > - * We need to tell lockdep that IRQs are off. We can't do this until
> > > - * we fix gsbase, and we should do it before enter_from_user_mode
> > > - * (which can take locks).
> > > - */
> > > - TRACE_IRQS_OFF
> >
> > This hunk looks wrong. Am I missing some other place that handles the
> > case where we enter from kernel mode and IRQs were on?
>
> > > - CALL_enter_from_user_mode
> > > ret
> > >
> > > .Lerror_entry_done:
> > > - TRACE_IRQS_OFF
> > > ret
> > >
> > > /*
>
> Did you perchance mean to complain about the .Lerror_entry_done one?

Yes, duh.

I would suggest compiling with DEBUG_LOCKDEP and running perf and the
x86 selftests. IIRC that's what catches most of the IRQ flag tracing
errors.

>
> Because I'm not seeing how the one before CALL_enter_from_user_mode can
> ever be from-kernel.
>
> But yes, that .Lerror_entry_done one looks fishy.

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