linux-kernel - Re: [PATCH net] neighbour: fix unaligned access to pneigh

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Message-ID: <CANn89iKRX2QTgS44Ky6Jua-+UNrFY3E7RCT_7OfG=GnFvAzdFQ@mail.gmail.com>
Date:   Wed, 31 May 2023 20:41:32 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Qingfang DENG <dqfext@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
        Ville Nuorvala <vnuorval@....hut.fi>,
        Masahide NAKAMURA <nakam@...ux-ipv6.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Qingfang DENG <qingfang.deng@...lower.com.cn>
Subject: Re: [PATCH net] neighbour: fix unaligned access to pneigh_entry

On Wed, May 31, 2023 at 8:16 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 31 May 2023 18:42:33 +0800 Qingfang DENG wrote:
> > +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> >       u8                      key[];
> > +#else
> > +     u8                      key[] __aligned(4);
> > +#endif
>
> I'd appreciate a second opinion, but to me it's very unlikely we'd save
> any memory even with efficient aligned access here. No reasonably key
> will fit into 3 bytes, right? So we can as well avoid the ifdef and
> make the key[] always aligned. Or preferably, if it doesn't cause
> compilation issues, make the type of the key u32?

Same feeling, we could avoid the CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS ifdef.