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

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Date:   Fri, 27 Mar 2020 20:17:52 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        Charles Daymand <charles.daymand@...irst.fr>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] r8169: fix multicast tx issue with macvlan interface

On 27.03.2020 19:52, Eric Dumazet wrote:
> 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()
> 
Thanks, Eric. There's a second path in macvlan_queue_xmit() calling
dev_forward_skb(vlan->lowerdev, skb). Does what you said apply also there?

Still I find it strange that a tx hw checksumming issue should affect multicasts
only. Also the chip version in question is quite common and I would expect
others to have hit the same issue.
Maybe best would be to re-test on the affected system w/o involving macvlen.

> 
> 
>> 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.