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SubjectRe: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled synchronisation with actual irq state
On Thu, Jul 23, 2020 at 11:11:03PM +1000, Nicholas Piggin wrote:
> Excerpts from Peter Zijlstra's message of July 23, 2020 9:40 pm:
> > On Thu, Jul 23, 2020 at 08:56:14PM +1000, Nicholas Piggin wrote:
> >
> >> diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
> >> index 3a0db7b0b46e..35060be09073 100644
> >> --- a/arch/powerpc/include/asm/hw_irq.h
> >> +++ b/arch/powerpc/include/asm/hw_irq.h
> >> @@ -200,17 +200,14 @@ static inline bool arch_irqs_disabled(void)
> >> #define powerpc_local_irq_pmu_save(flags) \
> >> do { \
> >> raw_local_irq_pmu_save(flags); \
> >> - trace_hardirqs_off(); \
> >> + if (!raw_irqs_disabled_flags(flags)) \
> >> + trace_hardirqs_off(); \
> >> } while(0)
> >> #define powerpc_local_irq_pmu_restore(flags) \
> >> do { \
> >> - if (raw_irqs_disabled_flags(flags)) { \
> >> - raw_local_irq_pmu_restore(flags); \
> >> - trace_hardirqs_off(); \
> >> - } else { \
> >> + if (!raw_irqs_disabled_flags(flags)) \
> >> trace_hardirqs_on(); \
> >> - raw_local_irq_pmu_restore(flags); \
> >> - } \
> >> + raw_local_irq_pmu_restore(flags); \
> >> } while(0)
> >
> > You shouldn't be calling lockdep from NMI context!
>
> After this patch it doesn't.

You sure, trace_hardirqs_{on,off}() calls into lockdep. (FWIW they're
also broken vs entry ordering, but that's another story).

> trace_hardirqs_on/off implementation appears to expect to be called in NMI
> context though, for some reason.

Hurpm, not sure.. I'll have to go grep arch code now :/ The generic NMI
code didn't touch that stuff.

Argh, yes, there might be broken there... damn! I'll go frob around.

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