linux-kernel - RE: [PATCH 0/2]: ARM: Enable THREAD_INFO_IN

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Message-ID: <87a6kuhnav.fsf@keithp.com>
Date:   Thu, 02 Sep 2021 10:58:32 -0700
From:   Keith Packard <keithp@...thp.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     linux-kernel@...r.kernel.org, Abbott Liu <liuwenliang@...wei.com>,
        Alexander Sverdlin <alexander.sverdlin@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Hartley Sweeten <hsweeten@...ionengravers.com>,
        Jens Axboe <axboe@...nel.dk>, Jian Cai <jiancai@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        Maninder Singh <maninder1.s@...sung.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nick Desaulniers <ndesaulniers@...ogle.com>,
        Nicolas Pitre <nico@...xnic.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Vaneet Narang <v.narang@...sung.com>,
        "Wolfram Sang (Renesas)" <wsa+renesas@...g-engineering.com>,
        YiFei Zhu <yifeifz2@...inois.edu>
Subject: RE: [PATCH 0/2]: ARM: Enable THREAD_INFO_IN_TASK

"Russell King (Oracle)" <linux@...linux.org.uk> writes:

> I think you're introducing a circular dependency with this for
> certain kernel configurations:
>
> E.g. Have you tried running this with CONFIG_CPU_V6 enabled?

That's very useful feedback -- no, I hadn't ever tried this
configuration (presumably the compiler would have complained).

> #define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())

I've read through the v6 architecture reference manual (again) and
cannot find any place to store either a per_cpu_offset or even a small
processor id, which I didn't find surprising as I would have expected it
to already be used for this purpose.

I'll re-spin the changes making them conditional on !CONFIG_CPU_V6,
unless someone has an idea of how to identify the current core in a
multi-core ARMv6 system.

-- 
-keith

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