[PATCH 00/18] random: Include <linux/percpu.h> and resolve circular include dependency

[Uros Bizjak]

On Thu, Sep 5, 2024 at 2:41 PM Andy Shevchenko
<andriy.shevchenko at linux.intel.com> wrote:
>
> On Thu, Sep 05, 2024 at 02:17:08PM +0200, Uros Bizjak wrote:
> > There were several attempts to resolve circular include dependency
> > after the addition of percpu.h: 1c9df907da83 ("random: fix circular
> > include dependency on arm64 after addition of percpu.h"), c0842fbc1b18
> > ("random32: move the pseudo-random 32-bit definitions to prandom.h") and
> > finally d9f29deb7fe8 ("prandom: Remove unused include") that completely
> > removes inclusion of <linux/percpu.h>.
> >
> > Due to legacy reasons, <linux/random.h> includes <linux/prandom.h>, but
> > with the commit entry remark:
> >
> > --quote--
> > A further cleanup step would be to remove this from <linux/random.h>
> > entirely, and make people who use the prandom infrastructure include
> > just the new header file.  That's a bit of a churn patch, but grepping
> > for "prandom_" and "next_pseudo_random32" "struct rnd_state" should
> > catch most users.
> >
> > But it turns out that that nice cleanup step is fairly painful, because
> > a _lot_ of code currently seems to depend on the implicit include of
> > <linux/random.h>, which can currently come in a lot of ways, including
> > such fairly core headfers as <linux/net.h>.
> >
> > So the "nice cleanup" part may or may never happen.
> > --/quote--
> >
> > __percpu tag is currently defined in include/linux/compiler_types.h,
> > so there is no direct need for the inclusion of <linux/percpu.h>.
> > However, in [1] we would like to repurpose __percpu tag as a named
> > address space qualifier, where __percpu macro uses defines from
> > <linux/percpu.h>.
> >
> > This patch series is the "nice cleanup" part, and allows us to finally
> > include <linux/percpu.h> in prandom.h.
> >
> > The whole series was tested by compiling the kernel for x86_64 allconfig
> > and some popular architectures, namely arm64 defconfig, powerpc defconfig
> > and loongarch defconfig.
>
> Obvious question(s) is(are):
> 1) have you seen the Ingo's gigantic patch series towards resolving issues with
> the headers?
> 2) if not, please look at the preliminary work and take something from there, I
> believe there are many useful changes already waiting for a couple of years to
> be applied.
>
> Because I haven't found any references nor mentions of that in the cover letter
> here and explanation why it was not taking into consideration.

I am aware of the series, but the patch takes only a small bite of it
and specifically resolves the inclusion of <linux/prandom.h> from
linux/random.h. The series fixes the missing inclusion of
<linux/prandom.h> in files that use pseudo-random function and it was
not meant to be a general header cleanup. The end goal is to allow us
to include <linux/percpu.h> in linux/prandom.h - which uses __percpu
tag without the correct include.

Thus, the patch series is only tangentially connected to Ingo's patch series.

Best regards,
Uros.