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SubjectRe: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled synchronisation with actual irq state
Excerpts from Peter Zijlstra's message of July 24, 2020 12:59 am:
> 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.

At least for irq enable/disable functions yes. NMI runs with
interrupts disabled so these will never call trace_hardirqs_on/off
after this patch.

> (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.
>

Thanks,
Nick

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