Messages in this thread Patch in this message | | | From | Willem de Bruijn <> | Date | Sun, 13 Feb 2022 23:27:57 -0500 | Subject | Re: [PATCH] gso: do not skip outer ip header in case of ipip and net_failover |
| |
On Sun, Feb 13, 2022 at 11:03 PM Tao Liu <thomas.liu@ucloud.cn> wrote: > > Sorry for bothering, just repost it. > > > 2022年2月14日 09:28,Willem de Bruijn <willemdebruijn.kernel@gmail.com> 写道: > > > > On Sun, Feb 13, 2022 at 10:10 AM Tao Liu <thomas.liu@ucloud.cn> wrote: > >> > >> We encouter a tcp drop issue in our cloud environment. Packet GROed in host > >> forwards to a VM virtio_net nic with net_failover enabled. VM acts as a > >> IPVS LB with ipip encapsulation. The full path like: > >> host gro -> vm virtio_net rx -> net_failover rx -> ipvs fullnat > >> -> ipip encap -> net_failover tx -> virtio_net tx > >> > >> When net_failover transmits a ipip pkt (gso_type = 0x0103), there is no gso > >> performed because it supports TSO and GSO_IPXIP4. But network_header has > >> been pointing to inner ip header. > > > > If the packet is configured correctly, and net_failover advertises > > that it can handle TSO packets with IPIP encap, then still virtio_net > > should not advertise it and software GSO be applied on its > > dev_queue_xmit call. > > > > This is assuming that the packet not only has SKB_GSO_IPXIP4 correctly > > set, but also tunneling fields like skb->encapsulated and > > skb_inner_network_header. > Thanks very much for your comment! > > Yes, the packet is correct. Another thing i have not pointed directly is > that the pkt has SKB_GSO_DODGY. net_failover do not advertises GSO_ROBUST > but virtio_net do.
If net_failover does not advertise NETIF_F_GSO_ROBUST, then tcp_gso_segment will pass a packet with SKB_GSO_DODGY to the software gso stack, not taking the branch
if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) {
> >> --- > >> net/ipv4/af_inet.c | 10 +++++++++- > >> 1 file changed, 9 insertions(+), 1 deletion(-) > >> > >> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c > >> index 9c465ba..f8b3f8a 100644 > >> --- a/net/ipv4/af_inet.c > >> +++ b/net/ipv4/af_inet.c > >> @@ -1425,10 +1425,18 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb, > >> static struct sk_buff *ipip_gso_segment(struct sk_buff *skb, > >> netdev_features_t features) > >> { > >> + struct sk_buff *segs; > >> + int nhoff; > >> + > >> if (!(skb_shinfo(skb)->gso_type & SKB_GSO_IPXIP4)) > >> return ERR_PTR(-EINVAL); > >> > >> - return inet_gso_segment(skb, features); > >> + nhoff = skb_network_header(skb) - skb_mac_header(skb); > >> + segs = inet_gso_segment(skb, features); > >> + if (!segs) > >> + skb->network_header = skb_mac_header(skb) + nhoff - skb->head; > >> + > >> + return segs; > >> } > > > > If this would be needed for IPIP, then the same would be needed for SIT, etc. > > > > Is the skb_network_header > > > > 1. correctly pointing to the outer header of the TSO packet before the > > call to inet_gso_segment > > 2. incorrectly pointing to the inner header of the (still) TSO packet > > after the call to inet_gso_segment > > > > inet_gso_segment already does the same operation: save nhoff, pull > > network header, call callbacks.gso_segment (which can be > > ipip_gso_segment->inet_gso_segment), then place the network header > > back at nhoff. > > > values print in skb_mac_gso_segment() before callbacks.gso_segment: > ipip: vlan_depth=0 mac_len=0 skb->network_header=206 > net_failover: vlan_depth=14 mac_len=14 skb->network_header=186 > virtio_net: vlan_depth=34 mac_len=34 skb->network_header=206 > > agree to add sit/ip4ip6/ip6ip6, and patch can be simplified as:
If IPIP GSO was so broken, I think we would have found it long before.
As said, inet_gso_segment should already do the right thing for ipip: it will be called twice.
| |