netdev - Re: [PATCH net] r8169: fix multicast tx issue with macvlan interface

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Date:   Fri, 27 Mar 2020 11:52:12 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Charles Daymand <charles.daymand@...irst.fr>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] r8169: fix multicast tx issue with macvlan interface

On Fri, Mar 27, 2020 at 10:41 AM Heiner Kallweit <hkallweit1@...il.com> wrote:
>
> On 27.03.2020 10:39, Heiner Kallweit wrote:
> > On 27.03.2020 10:08, Charles Daymand wrote:
> >> During kernel upgrade testing on our hardware, we found that macvlan
> >> interface were no longer able to send valid multicast packet.
> >>
> >> tcpdump run on our hardware was correctly showing our multicast
> >> packet but when connecting a laptop to our hardware we didn't see any
> >> packets.
> >>
> >> Bisecting turned up commit 93681cd7d94f
> >> "r8169: enable HW csum and TSO" activates the feature NETIF_F_IP_CSUM
> >> which is responsible for the drop of packet in case of macvlan
> >> interface. Note that revision RTL_GIGA_MAC_VER_34 was already a specific
> >> case since TSO was keep disabled.
> >>
> >> Deactivating NETIF_F_IP_CSUM using ethtool is correcting our multicast
> >> issue, but we believe that this hardware issue is important enough to
> >> keep tx checksum off by default on this revision.
> >>
> >> The change is deactivating the default value of NETIF_F_IP_CSUM for this
> >> specific revision.
> >>
> >
> > The referenced commit may not be the root cause but just reveal another
> > issue that has been existing before. Root cause may be in the net core
> > or somewhere else. Did you check with other RTL8168 versions to verify
> > that it's indeed a HW issue with this specific chip version?
> >
> > What you could do: Enable tx checksumming manually (via ethtool) on
> > older kernel versions and check whether they are fine or not.
> > If an older version is fine, then you can start a new bisect with tx
> > checksumming enabled.
> >
> > And did you capture and analyze traffic to verify that actually the
> > checksum is incorrect (and packets discarded therefore on receiving end)?
> >
> >
> >> Fixes: 93681cd7d94f ("r8169: enable HW csum and TSO")
> >> Signed-off-by: Charles Daymand <charles.daymand@...irst.fr>
> >> ---
> >>  net/drivers/net/ethernet/realtek/r8169_main.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/net/drivers/net/ethernet/realtek/r8169_main.c b/net/drivers/net/ethernet/realtek/r8169_main.c
> >> index a9bdafd15a35..3b69135fc500 100644
> >> --- a/net/drivers/net/ethernet/realtek/r8169_main.c
> >> +++ b/net/drivers/net/ethernet/realtek/r8169_main.c
> >> @@ -5591,6 +5591,9 @@ static int rtl_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
> >>              dev->vlan_features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);
> >>              dev->hw_features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);
> >>              dev->features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);
> >> +            if (tp->mac_version == RTL_GIGA_MAC_VER_34) {
> >> +                    dev->features &= ~NETIF_F_IP_CSUM;
> >> +            }
> >>      }
> >>
> >>      dev->hw_features |= NETIF_F_RXALL;
> >>
> >
>
> After looking a little bit at the macvlen code I think there might be an
> issue in it, but I'm not sure, therefore let me add Eric (as macvlen doesn't
> seem to have a dedicated maintainer).
>
> r8169 implements a ndo_features_check callback that disables tx checksumming
> for the chip version in question and small packets (due to a HW issue).
> macvlen uses passthru_features_check() as ndo_features_check callback, this
> seems to indicate to me that the ndo_features_check callback of lowerdev is
> ignored. This could explain the issue you see.
>

macvlan_queue_xmit() calls dev_queue_xmit_accel() after switching skb->dev,
so the second __dev_queue_xmit() should eventually call the real_dev
ndo_features_check()



> Would be interesting to see whether it fixes your issue if you let the
> macvlen ndo_features_check call lowerdev's ndo_features_check. Can you try this?
>
> By the way:
> Also the ndo_fix_features callback of lowerdev seems to be ignored.