Re: [PATCH] soc: samsung: exynos-pmu: Fix for CONFIG_DEBUG_PREEMPT

[Will Deacon <will@kernel.org>]

On Tue, Sep 09, 2025 at 05:43:16PM +0200, Krzysztof Kozlowski wrote:
> On 09/09/2025 12:15, Will Deacon wrote:
> > Krzysztof,
> > 
> > On Sat, Sep 06, 2025 at 09:07:02AM +0200, Krzysztof Kozlowski wrote:
> >> On 05/09/2025 19:43, Mostafa Saleh wrote:
> >>>>>
> >>>>> As this value is only read once, it doesn't require to be stable, so
> >>>>
> >>>> Why it does not need to be stable? Onlining wrong CPU number is not
> >>>> desired...
> >>>>
> >>>>> just use "raw_smp_processor_id" instead.
> >>>>
> >>>> You might be just hiding some other real issue, because above stacktrace
> >>>> is from gs101_cpuhp_pmu_online() which IRQs disabled and preemption
> >>>> disabled. Provide analysis of the warning, instead of just making it
> >>>> disappear.
> >>>
> >>> Not sure I understand, how is preemption disabled? that wouldn't fire
> >>> in that case.
> >>
> >> Because there is explicit preempt_disable().
> > 
> > Where do you see that?
> 
> I did look at the code.
> 
> All the calls I saw (including calltrace from commit msg) were under raw
> spinlock and raw spinlock does:
> 
> preempt_disable();

The backtrace doesn't contain a raw spinlock. As Peter subsequently
pointed out, the reported issue has been fixed in linux-next and there's
a raw spinlock there but since the report is from vanilla -rc4, it
doesn't have that fix.

Will