Re: [PATCH] virtio: Work around frames incorrectly marked as gso

[Jason Wang <jasowang@redhat.com>]

On 2020/2/13 上午1:38, Anton Ivanov wrote:
>
>
> On 11/02/2020 10:37, Michael S. Tsirkin wrote:
>> On Tue, Feb 11, 2020 at 07:42:37AM +0000, Anton Ivanov wrote:
>>> On 11/02/2020 02:51, Jason Wang wrote:
>>>>
>>>> On 2020/2/11 上午12:55, Anton Ivanov wrote:
>>>>>
>>>>>
>>>>> On 09/12/2019 10:48, anton.ivanov@cambridgegreys.com wrote:
>>>>>> From: Anton Ivanov <anton.ivanov@cambridgegreys.com>
>>>>>>
>>>>>> Some of the frames marked as GSO which arrive at
>>>>>> virtio_net_hdr_from_skb() have no GSO_TYPE, no
>>>>>> fragments (data_len = 0) and length significantly shorter
>>>>>> than the MTU (752 in my experiments).
>>>>>>
>>>>>> This is observed on raw sockets reading off vEth interfaces
>>>>>> in all 4.x and 5.x kernels I tested.
>>>>>>
>>>>>> These frames are reported as invalid while they are in fact
>>>>>> gso-less frames.
>>>>>>
>>>>>> This patch marks the vnet header as no-GSO for them instead
>>>>>> of reporting it as invalid.
>>>>>>
>>>>>> Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
>>>>>> ---
>>>>>>    include/linux/virtio_net.h | 8 ++++++--
>>>>>>    1 file changed, 6 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
>>>>>> index 0d1fe9297ac6..d90d5cff1b9a 100644
>>>>>> --- a/include/linux/virtio_net.h
>>>>>> +++ b/include/linux/virtio_net.h
>>>>>> @@ -112,8 +112,12 @@ static inline int
>>>>>> virtio_net_hdr_from_skb(const struct sk_buff *skb,
>>>>>>                hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
>>>>>>            else if (sinfo->gso_type & SKB_GSO_TCPV6)
>>>>>>                hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
>>>>>> -        else
>>>>>> -            return -EINVAL;
>>>>>> +        else {
>>>>>> +            if (skb->data_len == 0)
>>>>>> +                hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;
>>>>>> +            else
>>>>>> +                return -EINVAL;
>>>>>> +        }
>>>>>>            if (sinfo->gso_type & SKB_GSO_TCP_ECN)
>>>>>>                hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN;
>>>>>>        } else
>>>>>>
>>>>>
>>>>> ping.
>>>>>
>>>>
>>>> Do you mean gso_size is set but gso_type is not? Looks like a bug
>>>> elsewhere.
>>>>
>>>> Thanks
>>>>
>>>>
>>> Yes.
>>>
>>> I could not trace it where it is coming from.
>>>
>>> I see it when doing recvmmsg on raw sockets in the UML vector network
>>> drivers.
>>>
>>
>> I think we need to find the culprit and fix it there, lots of other 
>> things
>> can break otherwise.
>> Just printing out skb->dev->name should do the trick, no?
>
> The printk in virtio_net_hdr_from_skb says NULL.
>
> That is probably normal for a locally originated frame.
>
> I cannot reproduce this with network traffic by the way - it happens 
> only if the traffic is locally originated on the host.
>
> A,


Or maybe you can try add dump_stack() there.

Thanks