Re: [PATCH] hpet: Fix division by zero in hpet_time_div()

[Arnd Bergmann]

On Thu, Jul 11, 2019 at 1:20 PM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
> The base value in do_div() called by hpet_time_div() is truncated from
> unsigned long to uint32_t, resulting in a divide-by-zero exception.

Good catch!

> --- a/drivers/char/hpet.c
> +++ b/drivers/char/hpet.c
> @@ -567,7 +567,7 @@ static inline unsigned long hpet_time_div(struct hpets *hpets,
>         unsigned long long m;
>
>         m = hpets->hp_tick_freq + (dis >> 1);
> -       do_div(m, dis);
> +       div64_ul(m, dis);
>         return (unsigned long)m;
>  }

This still looks wrong to me: div64_ul() unlike do_div() does not
modify its argument, so you have to assign the output like

       return div64_ul(m, dis);

       Arnd