linux-kernel - Re: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled synchronisation with actual irq state

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Date:   Wed, 19 Aug 2020 20:39:13 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Nicholas Piggin <npiggin@...il.com>, peterz@...radead.org
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled
 synchronisation with actual irq state



On 19/08/2020 09:54, Nicholas Piggin wrote:
> Excerpts from peterz@...radead.org's message of August 19, 2020 1:41 am:
>> On Tue, Aug 18, 2020 at 05:22:33PM +1000, Nicholas Piggin wrote:
>>> Excerpts from peterz@...radead.org's message of August 12, 2020 8:35 pm:
>>>> On Wed, Aug 12, 2020 at 06:18:28PM +1000, Nicholas Piggin wrote:
>>>>> Excerpts from peterz@...radead.org's message of August 7, 2020 9:11 pm:
>>>>>>
>>>>>> What's wrong with something like this?
>>>>>>
>>>>>> AFAICT there's no reason to actually try and add IRQ tracing here, it's
>>>>>> just a hand full of instructions at the most.
>>>>>
>>>>> Because we may want to use that in other places as well, so it would
>>>>> be nice to have tracing.
>>>>>
>>>>> Hmm... also, I thought NMI context was free to call local_irq_save/restore
>>>>> anyway so the bug would still be there in those cases?
>>>>
>>>> NMI code has in_nmi() true, in which case the IRQ tracing is disabled
>>>> (except for x86 which has CONFIG_TRACE_IRQFLAGS_NMI).
>>>>
>>>
>>> That doesn't help. It doesn't fix the lockdep irq state going out of
>>> synch with the actual irq state. The code which triggered this with the
>>> special powerpc irq disable has in_nmi() true as well.
>>
>> Urgh, you're talking about using lockdep_assert_irqs*() from NMI
>> context?
>>
>> If not, I'm afraid I might've lost the plot a little on what exact
>> failure case we're talking about.
>>
> 
> Hm, I may have been a bit confused actually. Since your Fix 
> TRACE_IRQFLAGS vs NMIs patch it might now work.
> 
> I'm worried powerpc disables trace irqs trace_hardirqs_off()
> before nmi_enter() might still be a problem, but not sure
> actually. Alexey did you end up re-testing with Peter's patch

The one above in the thread which replaces powerpc_local_irq_pmu_save()
with
raw_powerpc_local_irq_pmu_save()? It did not compile as there is no
raw_powerpc_local_irq_pmu_save() so I may be missing something here.

I applied the patch on top of the current upstream and replaced
raw_powerpc_local_irq_pmu_save() with raw_local_irq_pmu_save()  (which I
think was the intention) but I still see the issue.

> or current upstream?

The upstream 18445bf405cb (13 hours old) also shows the problem. Yours
1/2 still fixes it.


> 
> Thanks,
> Nick
> 

-- 
Alexey