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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 5 Aug 2021 16:02:22 +0200
Message-ID: <CAK8P3a3aNuxaEtAiewd+Wjc8hKtca0NrcV2kykkNC-qKT_HhzQ@mail.gmail.com>
Subject: Re: [PATCH] rbtree: remove unneeded explicit alignment in struct rb_node
To:     Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc:     Michel Lespinasse <michel@lespinasse.org>,
        Davidlohr Bueso <dbueso@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mete Polat <metepolat2000@gmail.com>,
        Jesper Nilsson <jesper@jni.nu>, Arnd Bergmann <arnd@arndb.de>,
        David Woodhouse <dwmw2@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        kernel-janitors@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>
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Precedence: bulk

On Thu, Aug 5, 2021 at 3:32 PM Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote:
>
> Commit e977145aeaad ("[RBTREE] Add explicit alignment to sizeof(long) for
> struct rb_node.") adds an explicit alignment to the struct rb_node due to
> some speciality of the CRIS architecture.
>
> The support for the CRIS architecture was removed with commit c690eddc2f3b
> ("CRIS: Drop support for the CRIS port")
>
> So, remove this now unneeded explicit alignment in struct rb_node as well.
>
> This basically reverts commit e977145aeaad ("[RBTREE] Add explicit
> alignment to sizeof(long) for struct rb_node.").
>
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Reported-by: Mete Polat <metepolat2000@gmail.com>
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
> ---
> applies cleanly on next-20210804, but only x86 compile-checked.
>
> Michel, Davidlohr, Jesper, David, please ack.
>
> Mete, you might want to re-run your RBT test suite for this change.
>
> Andrew, once acked, please pick this minor cleanup into your tree.

Do you know why it needed the extra alignment on cris at the time?

The revert would appear to change the alignment to 16 bits instead
of 32 bits on m68k as well (not 8 bits as on cris), but I don't know if that
can cause problems there.

        Arnd