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SubjectRe: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled synchronisation with actual irq state
Excerpts from Alexey Kardashevskiy's message of July 24, 2020 2:16 pm:
>
>
> On 23/07/2020 23:11, 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.
>>
>> trace_hardirqs_on/off implementation appears to expect to be called in NMI
>> context though, for some reason.
>>
>>> 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.
>>
>> Hmm. My patch seems simpler.
>
> And your patches fix my error while Peter's do not:
>
>
> IRQs not enabled as expected
> WARNING: CPU: 0 PID: 1377 at /home/aik/p/kernel/kernel/softirq.c:169
> __local_bh_enable_ip+0x118/0x190

I think they would have needed some powerpc bits as well. But I don't
see a reason we can't merge my patches, at least they fix this case and
don't seem to make things worse in any way.

Thanks,
Nick

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