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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 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! That is, I recently
added suport for that on x86:

https://lkml.kernel.org/r/20200623083721.155449112@infradead.org
https://lkml.kernel.org/r/20200623083721.216740948@infradead.org

But you need to be very careful on how you order things, as you can see
the above relies on preempt_count() already having been incremented with
NMI_MASK.

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