Re: [PATCH RESEND2] lib: fix bitmap_parse() on 64-bit big endian archs

[Andy Shevchenko]

On Mon, Jun 8, 2020 at 1:26 PM Alexander Gordeev <agordeev@xxxxxxxxxxxxx> wrote:
>
> Commit 2d6261583be0 ("lib: rework bitmap_parse()") does not
> take into account order of halfwords on 64-bit big endian
> architectures. As result (at least) Receive Packet Steering,
> IRQ affinity masks and runtime kernel test "test_bitmap" get
> broken on s390.

...

> +#if defined(__BIG_ENDIAN) && defined(CONFIG_64BIT)

I think it's better to re-use existing patterns.

ipc/sem.c:1682:#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)

> +static void save_x32_chunk(unsigned long *maskp, u32 chunk, int chunk_idx)
> +{
> +       maskp += (chunk_idx / 2);
> +       ((u32 *)maskp)[(chunk_idx & 1) ^ 1] = chunk;
> +}
> +#else
> +static void save_x32_chunk(unsigned long *maskp, u32 chunk, int chunk_idx)
> +{
> +       ((u32 *)maskp)[chunk_idx] = chunk;
> +}
> +#endif

See below.

...

> -               end = bitmap_get_x32_reverse(start, end, bitmap++);
> +               end = bitmap_get_x32_reverse(start, end, &chunk);
>                 if (IS_ERR(end))
>                         return PTR_ERR(end);
> +
> +               save_x32_chunk(maskp, chunk, chunk_idx++);

Can't we simple do

        int chunk_index = 0;
        ...
        do {
#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
               end = bitmap_get_x32_reverse(start, end,
bitmap[chunk_index ^ 1]);
#else
               end = bitmap_get_x32_reverse(start, end, bitmap[chunk_index]);
#endif
        ...
        } while (++chunk_index);

?

-- 
With Best Regards,
Andy Shevchenko