Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200424121051.5056-1-geert@linux-m68k.org> <d2c14a2d-4e7b-d36a-be90-e987b1ea6183@gmail.com>
In-Reply-To: <d2c14a2d-4e7b-d36a-be90-e987b1ea6183@gmail.com>
From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Fri, 24 Apr 2020 17:12:46 +0200
Message-ID: <CAMuHMdWVmP04cXEgAkOc9Qdb2Y2xjGd1YEOcMt7ehE70ZwdqjQ@mail.gmail.com>
Subject: Re: [PATCH] net: openvswitch: use do_div() for 64-by-32 divisions:
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Pravin B Shelar <pshelar@ovn.org>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Tonghao Zhang <xiangxia.m.yue@gmail.com>,
        netdev <netdev@vger.kernel.org>, dev@openvswitch.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Eric,

On Fri, Apr 24, 2020 at 5:05 PM Eric Dumazet <eric.dumazet@gmail.com> 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@ellerman.id.au
> > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> > ---
> >  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.

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