Re: [PATCH v3 16/16] ARM: Remove custom IRQ stat accounting

Guillaume Tucker
2020-09-28T09:01:00Z

Hi Marc,

On 24/09/2020 14:09, Guillaume Tucker wrote:
> On 24/09/2020 10:29, Marc Zyngier wrote:
>> Hi Guillaume,
>>
>> On Thu, 24 Sep 2020 10:00:09 +0100,
>> Guillaume Tucker <guillaume.tucker@collabora.com> wrote:
>>>
>>> Hi Marc,
>>>
>>> On 01/09/2020 15:43, Marc Zyngier wrote:
>>>> Let's switch the arm code to the core accounting, which already
>>>> does everything we need.
>>>>
>>>> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
>>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>>> ---
>>>> arch/arm/include/asm/hardirq.h | 17 -----------------
>>>> arch/arm/kernel/smp.c | 20 ++++----------------
>>>> 2 files changed, 4 insertions(+), 33 deletions(-)
>>>
>>> This appears to be causing a NULL pointer dereference on
>>> beaglebone-black, it got bisected automatically several times.
>>> None of the other platforms in the KernelCI labs appears to be
>>> affected.
>>
>> Hmm. My bet is that because this is a UP machine running an SMP
>> kernel, and I fell into the trap of forgetting about this 32bit
>> configuration.
>>
>> I expect the following patch to fix it. Please give it a go if you can
>> (I'm away at the moment and can't test much, and do not have any
>> physical 32bit machine to test this on).
>
> OK thanks, that worked:
>
> https://lava.baylibre.com/scheduler/job/143170
>
> I've added this fix to the kernel branch used on
> staging.kernelci.org which is based on linux-next, so it will get
> fully verified a bit later today.
>
> Guillaume
>
>
>> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
>> index 00327fa74b01..b4e3d336dc33 100644
>> --- a/arch/arm/kernel/smp.c
>> +++ b/arch/arm/kernel/smp.c
>> @@ -531,7 +531,12 @@ void show_ipi_list(struct seq_file *p, int prec)
>> unsigned int cpu, i;
>>
>> for (i = 0; i < NR_IPI; i++) {
>> - unsigned int irq = irq_desc_get_irq(ipi_desc[i]);
>> + unsigned int irq;
>> +
>> + if (!ipi_desc[i])
>> + continue;
>> +
>> + irq = irq_desc_get_irq(ipi_desc[i]);
>> seq_printf(p, "%*s%u: ", prec - 1, "IPI", i);
>>
>> for_each_online_cpu(cpu)

This fix has been all tested now, with no visible side effects:

https://staging.kernelci.org/test/job/kernelci/branch/staging.kernelci.org/kernel/staging-20200928.1/plan/baseline/

In the meantime, the same issue was detected (without the fix)
and bisected on sun5i-a13-olinuxino-micro and landed on the same
commit. A few more platforms are also impacted such as imx53-qsb
as mentioned by Fabio.

The commit is in your irqchip tree so I guess we should wait for
you to apply the fix. If you do make a separate commit to fix
the issue, please add:

Reported-by: kernelci.org bot <bot@kernelci.org>

and also:

Tested-by: Guillaume Tucker <guillaume.tucker@collabora.com>

Thanks,
Guillaume