Re: [PATCH] atomic{64}_t: Explicitly specify data storage length and alignment

[Geert Uytterhoeven]

Hi Alexey,

On Mon, Jul 9, 2018 at 2:48 PM Alexey Brodkin
<Alexey.Brodkin@xxxxxxxxxxxx> wrote:
> Atomic instructions require data they operate on to be aligned
> according to data size. I.e. 32-bit atomic values must be 32-bit
> aligned while 64-bit values must be 64-bit aligned.
>
> Otherwise even if CPU may handle not-aligend normal data access,
> still atomic instructions fail and typically raise an exception
> leaving us dead in the water.
>
> This came-up during lengthly discussion here:
> http://lists.infradead.org/pipermail/linux-snps-arc/2018-July/004022.html
>
> Signed-off-by: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>

Thanks for your patch!

> --- a/include/asm-generic/atomic64.h
> +++ b/include/asm-generic/atomic64.h
> @@ -13,7 +13,7 @@
>  #define _ASM_GENERIC_ATOMIC64_H
>
>  typedef struct {
> -       long long counter;
> +       u64 __aligned(8) counter;

I think you can drop the change to this file, as this is the generic
implementation using spinlocks, for processors that don't have 64-bit atomic
instructions.

>  } atomic64_t;

Reviewed-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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