linux-kernel - Re: [PATCH 1/4] btrfs: fix 64bit division in btrfs_insert_striped_mirrored_raid

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Message-ID: <CAMuHMdWM3_cj4Nb96pZQfErx7n+0Cd7RUQZV+bpvr1Tz5T3sgw@mail.gmail.com>
Date:   Mon, 18 Sep 2023 16:18:53 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Johannes Thumshirn <johannes.thumshirn@....com>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, Qu Wenru <wqu@...e.com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] btrfs: fix 64bit division in btrfs_insert_striped_mirrored_raid_extents

Hi Johannes,

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