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

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Message-ID: <Ztmm00eLBQGtiwRM@smile.fi.intel.com>
Date: Thu, 5 Sep 2024 15:40:51 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Uros Bizjak <ubizjak@...il.com>
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Subject: Re: [PATCH 00/18] random: Include <linux/percpu.h> and resolve
 circular include dependency

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.

> [1] https://lore.kernel.org/lkml/20240812115945.484051-4-ubizjak@gmail.com/

-- 
With Best Regards,
Andy Shevchenko