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Message-ID: <CAFULd4bzyNGcJqeg7w2ZQ0Xmw-HsBhczf8yPna7mSgG4NmdcWw@mail.gmail.com>
Date: Thu, 5 Sep 2024 15:03:24 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Jani Nikula <jani.nikula@...ux.intel.com>, 
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
	Tvrtko Ursulin <tursulin@...ulin.net>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	Hans Verkuil <hverkuil@...all.nl>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Miquel Raynal <miquel.raynal@...tlin.com>, Richard Weinberger <richard@....at>, 
	Vignesh Raghavendra <vigneshr@...com>, Eric Biggers <ebiggers@...nel.org>, 
	"Theodore Y. Ts'o" <tytso@....edu>, Jaegeuk Kim <jaegeuk@...nel.org>, 
	"Jason A. Donenfeld" <Jason@...c4.com>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Hannes Reinecke <hare@...e.de>, 
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>, 
	"Martin K. Petersen" <martin.petersen@...cle.com>, Alexei Starovoitov <ast@...nel.org>, 
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	Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
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	Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Stephen Hemminger <stephen@...workplumber.org>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Kent Overstreet <kent.overstreet@...ux.dev>, 
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
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	bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	kunit-dev@...glegroups.com
Subject: Re: [PATCH 00/18] random: Include <linux/percpu.h> and resolve
 circular include dependency

On Thu, Sep 5, 2024 at 2:41 PM Andy Shevchenko
<andriy.shevchenko@...ux.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.

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