Re: [PATCH] percpu: fix clang modpost warning in pcpu_build_alloc_info()

[Arnd Bergmann]

On Tue, Jan 5, 2021 at 1:55 AM Dennis Zhou <dennis@xxxxxxxxxx> wrote:
>
> On Mon, Jan 04, 2021 at 04:46:51PM -0700, Nathan Chancellor wrote:
> > On Thu, Dec 31, 2020 at 09:28:52PM +0000, Dennis Zhou wrote:
> > >
>
> Hi Nathan,
>
> >
> > Hi Dennis,
> >
> > I did a bisect of the problematic config against defconfig and it points
> > out that CONFIG_GCOV_PROFILE_ALL is in the bad config but not the good
> > config, which makes some sense as that will mess with clang's inlining
> > heuristics. It does not appear to be the single config that makes a
> > difference but it gives some clarity.
> >
>
> Ah, thanks. To me it's kind of a corner case that I don't have a lot of
> insight into. __init code is pretty limited and this warning is really
> at the compilers whim. However, in this case only clang throws this
> warning.
>
> > I do not personally have any strong opinions around the patch but is it
> > really that much wasted memory to just annotate mask with __refdata?
>
> It's really not much memory, 1 bit per max # of cpus. The reported
> config is on the extreme side compiling with 8k NR_CPUS, so 1kb. I'm
> just not in love with the idea of adding a patch to improve readability
> and it cost idle memory to resolve a compile time warning.
>
> If no one else chimes in in the next few days, I'll probably just apply
> it and go from there. If another issue comes up I'll drop this and tag
> it as __refdata.

I've come across this one again in linux-next today, and found that
I had an old patch for it already, that I had never submitted: