Re: [PATCH] net: openvswitch: use do_div() for 64-by-32 divisions:

[Tonghao Zhang]

On Sat, Apr 25, 2020 at 1:54 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>
> Hi Toke,
>
> On Fri, Apr 24, 2020 at 6:45 PM Toke HÃiland-JÃrgensen <toke@xxxxxxxxxx> wrote:
> > Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> writes:
> > > On Fri, Apr 24, 2020 at 5:05 PM Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> > >> On 4/24/20 5:10 AM, Geert Uytterhoeven wrote:
> > >> > On 32-bit architectures (e.g. m68k):
> > >> >
> > >> >     ERROR: modpost: "__udivdi3" [net/openvswitch/openvswitch.ko] undefined!
> > >> >     ERROR: modpost: "__divdi3" [net/openvswitch/openvswitch.ko] undefined!
> > >> >
> > >> > Fixes: e57358873bb5d6ca ("net: openvswitch: use u64 for meter bucket")
> > >> > Reported-by: noreply@xxxxxxxxxxxxxx
> > >> > Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > >> > ---
> > >> >  net/openvswitch/meter.c | 2 +-
> > >> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >> >
> > >> > diff --git a/net/openvswitch/meter.c b/net/openvswitch/meter.c
> > >> > index 915f31123f235c03..3498a5ab092ab2b8 100644
> > >> > --- a/net/openvswitch/meter.c
> > >> > +++ b/net/openvswitch/meter.c
> > >> > @@ -393,7 +393,7 @@ static struct dp_meter *dp_meter_create(struct nlattr **a)
> > >> >                * Start with a full bucket.
> > >> >                */
> > >> >               band->bucket = (band->burst_size + band->rate) * 1000ULL;
> > >> > -             band_max_delta_t = band->bucket / band->rate;
> > >> > +             band_max_delta_t = do_div(band->bucket, band->rate);
> > >> >               if (band_max_delta_t > meter->max_delta_t)
> > >> >                       meter->max_delta_t = band_max_delta_t;
> > >> >               band++;
> > >> >
> > >>
> > >> This is fascinating... Have you tested this patch ?
> > >
> > > Sorry, I should have said this is compile-tested only.
> > >
> > >> Please double check what do_div() return value is supposed to be !
> > >
> > > I do not have any openvswitch setups, let alone on the poor m68k box.
> >
> > I think what Eric is referring to is this, from the documentation of
> > do_div:
> >
> >  * do_div - returns 2 values: calculate remainder and update new dividend
> >  * @n: uint64_t dividend (will be updated)
> >  * @base: uint32_t divisor
> >  *
> >  * Summary:
> >  * ``uint32_t remainder = n % base;``
> >  * ``n = n / base;``
> >  *
> >  * Return: (uint32_t)remainder
>
> Oops, that was a serious brain fart. Sorry for that!
>
> That should have been div_u64() instead of do_div().
> Feel free to update my patch while applying, else I'll send a v2 later.
>
> /me hides in a brown paper bag for the whole weekend...
I sent the patch with updated, change the reported tag, test it, and
add more commit msg,
and author should be you. Thanks.
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> 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



-- 
Best regards, Tonghao