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

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Date:   Fri, 27 Mar 2020 18:41:31 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Charles Daymand <charles.daymand@...irst.fr>,
        netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] r8169: fix multicast tx issue with macvlan interface

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.

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.