linux-kernel - Re: [RESEND PATCH v2] devres: Really align data field to unsigned long long

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Date:   Mon, 9 Jul 2018 09:52:56 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        stable <stable@...r.kernel.org>, Greg KH <greg@...ah.com>,
        arcml <linux-snps-arc@...ts.infradead.org>
Subject: Re: [RESEND PATCH v2] devres: Really align data field to unsigned
 long long

Hi Alexey,

On Mon, Jul 9, 2018 at 9:22 AM Alexey Brodkin
<Alexey.Brodkin@...opsys.com> wrote:
> On Mon, 2018-07-09 at 09:07 +0200, Geert Uytterhoeven wrote:
> > On Mon, Jul 9, 2018 at 7:49 AM Greg KH <greg@...ah.com> wrote:
> > > On Mon, Jul 09, 2018 at 07:44:44AM +0300, Alexey Brodkin wrote:
> > > > Depending on ABI "long long" type of a particular 32-bit CPU
> > > > might be aligned by either word (32-bits) or double word (64-bits).
> >
> > Or even 16-bit (on e.g. m68k).
>
> Indeed, thanks for the note!
> Will add this in my v3.

Note that in this particular case, the field will probably always be
aligned to 4 bytes,
as the struct will be allocated using *alloc().

> For ARC I'd like this fix to be back-ported starting
> from v4.8 where we added support of "native" atomic64_t, see commit
> ce6365270ecd (" ARCv2: Implement atomic64 based on LLOCKD/SCONDD instructions").
>
> What about m68k, do you have any preference of earliest kernel version
> where this fix might be useful?

Given m68k is 32-bit, it will access atomic64_t variables while
holding a spinlock,
so it should still be safe without this change.

Not to mention no one will try etnaviv on m68k ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds