Re: [PATCH RESEND 1/1] lib/Kconfig: remove DEBUG_PER_CPU_MAPS dependency for CPUMASK_OFFSTACK

[Libo Chen]

Hi Randy,

On 4/12/22 17:18, Randy Dunlap wrote:
> Hi--
>
> On 4/12/22 16:15, Libo Chen wrote:
> > Forcing CPUMASK_OFFSTACK to be conditoned on DEBUG_PER_CPU_MAPS doesn't
> > make a lot of sense nowaday. Even the original patch dating back to 2008,
> > aab46da0520a ("cpumask: Add CONFIG_CPUMASK_OFFSTACK") didn't give any
> > rationale for such dependency.
> >
> > Nowhere in the code supports the presumption that DEBUG_PER_CPU_MAPS is
> > necessary for CONFIG_CPUMASK_OFFSTACK. Make no mistake, it's good to
> > have DEBUG_PER_CPU_MAPS for debugging purpose or precaution, but it's
> > simply not a hard requirement for CPUMASK_OFFSTACK. Moreover, x86 Kconfig
> > already can set CPUMASK_OFFSTACK=y without DEBUG_PER_CPU_MAPS=y.
> > There is no reason other architectures cannot given the fact that they
> > have even fewer, if any, arch-specific CONFIG_DEBUG_PER_CPU_MAPS code than
> > x86.
> >
> > Signed-off-by: Libo Chen <libo.chen@xxxxxxxxxx>
> > ---
> >   lib/Kconfig | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/Kconfig b/lib/Kconfig
> > index 087e06b4cdfd..7209039dfb59 100644
> > --- a/lib/Kconfig
> > +++ b/lib/Kconfig
> > @@ -511,7 +511,7 @@ config CHECK_SIGNATURE
> >   	bool
> >   
> >   config CPUMASK_OFFSTACK
> > -	bool "Force CPU masks off stack" if DEBUG_PER_CPU_MAPS
> This "if" dependency only controls whether the Kconfig symbol's prompt is
> displayed (presented) in kconfig tools. Removing it makes the prompt always
> be displayed.
>
> Any architecture could select (should be able to) CPUMASK_OFFSTACK independently
> of DEBUG_PER_CPU_MAPS.
Do you mean changing arch/xxxx/Kconfig to select CPUMASK_OFFSTACK under 
some config xxx? That will work but it requires code changes for each 
architecture.
But if you are talking about setting CONFIG_CPUMASK_OFFSTACK=y without 
CONFIG_DEBUG_PER_CPU_MAPS directly in config file, I have tried, it 
doesn't work.

Libo
> Is there another problem here?
>
> > +	bool "Force CPU masks off stack"
> >   	help
> >   	  Use dynamic allocation for cpumask_var_t, instead of putting
> >   	  them on the stack.  This is a bit more expensive, but avoids