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SubjectRe: [PATCH net-next v3 1/2] net: dsa: untag the bridge pvid from rx skbs
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On 9/23/2020 4:08 PM, Vladimir Oltean wrote:
> On Wed, Sep 23, 2020 at 03:59:46PM -0700, Florian Fainelli wrote:
>> On 9/23/20 3:58 PM, Vladimir Oltean wrote:
>>> On Wed, Sep 23, 2020 at 03:54:59PM -0700, Florian Fainelli wrote:
>>>> Not having much luck with using __vlan_find_dev_deep_rcu() for a reason
>>>> I don't understand we trip over the proto value being neither of the two
>>>> support Ethertype and hit the BUG().
>>>>
>>>> + upper_dev = __vlan_find_dev_deep_rcu(br, htons(proto), vid);
>>>> + if (upper_dev)
>>>> + return skb;
>>>>
>>>> Any ideas?
>>>
>>> Damn...
>>> Yes, of course, the skb->protocol is still ETH_P_XDSA which is where
>>> eth_type_trans() on the master left it.
>>
>> proto was obtained from br_vlan_get_proto() a few lines above, and
>> br_vlan_get_proto() just returns br->vlan_proto which defaults to
>> htons(ETH_P_8021Q) from br_vlan_init().
>>
>> This is not skb->protocol that we are looking at AFAICT.
>
> Ok, my mistake. So what is the value of proto in vlan_proto_idx when it
> fails? To me, the call path looks pretty pass-through for vlan_proto.

At the time we crash the proto value is indeed ETH_P_XDSA, but it is not
because of the __vlan_find_dev_deep_rcu() call as I was mislead by the
traces I was looking it (on ARMv7 the LR was pointing not where I was
expecting it to), it is because of the following call trace:

netif_receive_skb_list_internal
-> __netif_receive_skb_list_core
-> __netif_receive_skb_core
-> vlan_do_receive()

That function does use skb->vlan_proto to determine the VLAN group, at
that point we have not set it but we did inherit skb->protocol instead
which is ETH_P_XDSA.

The following does work though, tested with both br0 and a br0.1 upper:

+ upper_dev = __vlan_find_dev_deep_rcu(br, htons(proto), vid);
+ if (upper_dev) {
+ skb->vlan_proto = vlan_dev_vlan_proto(upper_dev);
+ return skb;
}

I should have re-tested v2 and v3 with a bridge upper but I did not
otherwise I would have caught that. If that sounds acceptable to you as
well, I will submit that tomorrow.

Let me know what you think about the 802.1Q upper of a physical switch
port in the other email.
--
Florian

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