On 2019/1/29 12:01, Tom Herbert wrote:
> On Mon, Jan 28, 2019 at 7:00 PM maowenan <maowe...@huawei.com> wrote:
>>
>> Hi all，
>> Do you have any comments about this change?
>>
>>
>> On 2019/1/23 11:33, Mao Wenan wrote:
>>> When udp4_gro_receive() get one packet that uh->check=0,
>>> skb_gro_checksum_validate_zero_check() will set the
>>> skb->ip_summed = CHECKSUM_UNNECESSARY;
>>> skb->csum_level = 0;
>>> Then udp_gro_receive() will flush the packet which is not CHECKSUM_PARTIAL,
>>> It is not our expect, because check=0 in udp header indicates this
>>> packet is no need to caculate checksum, we should go further to do GRO.
>>>
>>> This patch changes the value of csum_cnt according to skb->csum_level.
>>> ---
>>> include/linux/netdevice.h | 1 +
>>> 1 file changed, 1 insertion(+)
>>>
>>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>>> index 1377d08..9c819f1 100644
>>> --- a/include/linux/netdevice.h
>>> +++ b/include/linux/netdevice.h
>>> @@ -2764,6 +2764,7 @@ static inline void
>>> skb_gro_incr_csum_unnecessary(struct sk_buff *skb)
>>> * during GRO. This saves work if we fallback to normal path.
>>> */
>>> __skb_incr_checksum_unnecessary(skb);
>>> + NAPI_GRO_CB(skb)->csum_cnt = skb->csum_level + 1;
>
> That doesn't look right. This would be reinitializing the GRO
> checksums from the beginning.
>
>>> }
>>> }
>>>
>>>
>>
> I assume the code is bailing on this conditional:
>
> if (NAPI_GRO_CB(skb)->encap_mark ||
> (skb->ip_summed != CHECKSUM_PARTIAL &&
> NAPI_GRO_CB(skb)->csum_cnt == 0 &&
> !NAPI_GRO_CB(skb)->csum_valid) ||
> !udp_sk(sk)->gro_receive)
> goto out_unlock;
>
> I am trying to remember why this needs to check csum_cnt. If there was
> a csum_cnt for the UDP csum being zero from checksum-unnecessary, it
> was consumed by skb_gro_checksum_validate_zero_check in UDP4 GRO
> received.
We have met the scene about two VMs in different host with vxlan packets, when
udp4_gro_receive receives
one packet with ip_summed=CHECKSUM_NONE,csum_cnt=0,csum_valid=0,and
udp->check=0, then skb_gro_checksum_validate_zero_check()->
skb_gro_incr_csum_unnecessary() validate it and set
ip_summed=CHECKSUM_UNNECESSARY,csum_level=0, but csum_cnt and csum_valid
keep zero value. Then it will be flushed in udp_gro_receive(), the codes as you
have showed.
so I think it forgets to modify csum_cnt since csum_level is changed in
skb_gro_incr_csum_unnecessary()->__skb_incr_checksum_unnecessary().
>
> .
>
