Re: [PATCH 1/4] btrfs: fix 64bit division in btrfs_insert_striped_mirrored_raid_extents

Geert Uytterhoeven
2023-09-18T15:23:53Z

Hi Johannes,

On Mon, Sep 18, 2023 at 4:14 PM Johannes Thumshirn
<johannes.thumshirn@wdc.com> wrote:
> Fix modpost error due to 64bit division on 32bit systems in
> btrfs_insert_striped_mirrored_raid_extents.
>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Thanks for your patch!

> --- a/fs/btrfs/raid-stripe-tree.c
> +++ b/fs/btrfs/raid-stripe-tree.c
> @@ -148,10 +148,10 @@ static int btrfs_insert_striped_mirrored_raid_extents(
> {
> struct btrfs_io_context *bioc;
> struct btrfs_io_context *rbioc;
> - const int nstripes = list_count_nodes(&ordered->bioc_list);
> - const int index = btrfs_bg_flags_to_raid_index(map_type);
> - const int substripes = btrfs_raid_array[index].sub_stripes;
> - const int max_stripes = trans->fs_info->fs_devices->rw_devices / substripes;
> + const size_t nstripes = list_count_nodes(&ordered->bioc_list);
> + const enum btrfs_raid_types index = btrfs_bg_flags_to_raid_index(map_type);
> + const u8 substripes = btrfs_raid_array[index].sub_stripes;
> + const int max_stripes = div_u64(trans->fs_info->fs_devices->rw_devices, substripes);

What if the quotient does not fit in a signed 32-bit value?

> int left = nstripes;
> int i;
> int ret = 0;

Gr{oetje,eeting}s,

Geert

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