Re: [RFC PATCH v1 18/50] net/ipv6/addrconf.c: Use prandom_u32_max for rfc3315 backoff time computation

[Maciej Åenczykowski]

>         /* multiply 'initial retransmission time' by 0.9 .. 1.1 */
> -       u64 tmp = (900000 + prandom_u32() % 200001) * (u64)irt;
> -       do_div(tmp, 1000000);
> -       return (s32)tmp;
> +       s32 range = irt / 5;
> +       return irt - (s32)(range/2) + (s32)prandom_u32_max(range);

The cast on range/2 looks entirely spurious

>         /* multiply 'retransmission timeout' by 1.9 .. 2.1 */
> -       u64 tmp = (1900000 + prandom_u32() % 200001) * (u64)rt;
> -       do_div(tmp, 1000000);
> -       if ((s32)tmp > mrt) {
> +       s32 range = rt / 5;
> +       s32 tmp = 2*rt - (s32)(range/2) + (s32)prandom_u32_max(range);

Here as well.  Honestly the cast on prandom might also not be
necessary, but that at least has a reason.

> +       if (tmp > mrt) {
>                 /* multiply 'maximum retransmission time' by 0.9 .. 1.1 */
> -               tmp = (900000 + prandom_u32() % 200001) * (u64)mrt;
> -               do_div(tmp, 1000000);
> +               range = mrt / 5;
> +               tmp = mrt - (s32)(range/2) + (s32)prandom_u32_max(range);

Ditto.

>         }
>         return (s32)tmp;
>  }

- Maciej