Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 5 Aug 2021 17:10:08 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Davidlohr Bueso <dbueso@suse.de>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        Michel Lespinasse <michel@lespinasse.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mete Polat <metepolat2000@gmail.com>,
        Jesper Nilsson <jesper@jni.nu>,
        David Woodhouse <dwmw2@infradead.org>,
        Ingo Molnar <mingo@kernel.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>
Subject: Re: [PATCH] rbtree: remove unneeded explicit alignment in struct
 rb_node
Message-ID: <YQv/UGiAddAS1T77@hirez.programming.kicks-ass.net>
References: <20210805133213.700-1-lukas.bulwahn@gmail.com>
 <CAK8P3a3aNuxaEtAiewd+Wjc8hKtca0NrcV2kykkNC-qKT_HhzQ@mail.gmail.com>
 <50ad4c8b848bd371b4b42959167ef03d@suse.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <50ad4c8b848bd371b4b42959167ef03d@suse.de>
Precedence: bulk

On Thu, Aug 05, 2021 at 08:02:28AM -0700, Davidlohr Bueso wrote:
> On 2021-08-05 07:02, Arnd Bergmann wrote:
> > 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.
> 
> Yeah I tried this a while back and it broke m68k, so it was a no go:
> 
> https://lore.kernel.org/lkml/CAMuHMdXeZvJ0X6Ah2CpLRoQJm+YhxAWBt-rUpxoyfOLTcHp+0g@mail.gmail.com/

I'm still thinking that any architecture that doesn't respect natural
alignment is playing with fire. For giggles we should put a runtime
alignment check in READ_ONCE() and see what goes *bang*.