| Message ID | 20240516200941.16152-1-aconole@redhat.com |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | [ovs-dev,v2,net] openvswitch: Set the skbuff pkt_type for proper pmtud support. | expand |
On 16 May 2024, at 22:09, Aaron Conole wrote: > Open vSwitch is originally intended to switch at layer 2, only dealing with > Ethernet frames. With the introduction of l3 tunnels support, it crossed > into the realm of needing to care a bit about some routing details when > making forwarding decisions. If an oversized packet would need to be > fragmented during this forwarding decision, there is a chance for pmtu > to get involved and generate a routing exception. This is gated by the > skbuff->pkt_type field. > > When a flow is already loaded into the openvswitch module this field is > set up and transitioned properly as a packet moves from one port to > another. In the case that a packet execute is invoked after a flow is > newly installed this field is not properly initialized. This causes the > pmtud mechanism to omit sending the required exception messages across > the tunnel boundary and a second attempt needs to be made to make sure > that the routing exception is properly setup. To fix this, we set the > outgoing packet's pkt_type to PACKET_OUTGOING, since it can only get > to the openvswitch module via a port device or packet command. > > Even for bridge ports as users, the pkt_type needs to be reset when > doing the transmit as the packet is truly outgoing and routing needs > to get involved post packet transformations, in the case of > VXLAN/GENEVE/udp-tunnel packets. In general, the pkt_type on output > gets ignored, since we go straight to the driver, but in the case of > tunnel ports they go through IP routing layer. > > This issue is periodically encountered in complex setups, such as large > openshift deployments, where multiple sets of tunnel traversal occurs. > A way to recreate this is with the ovn-heater project that can setup > a networking environment which mimics such large deployments. We need > larger environments for this because we need to ensure that flow > misses occur. In these environment, without this patch, we can see: > > ./ovn_cluster.sh start > podman exec ovn-chassis-1 ip r a 170.168.0.5/32 dev eth1 mtu 1200 > podman exec ovn-chassis-1 ip netns exec sw01p1 ip r flush cache > podman exec ovn-chassis-1 ip netns exec sw01p1 \ > ping 21.0.0.3 -M do -s 1300 -c2 > PING 21.0.0.3 (21.0.0.3) 1300(1328) bytes of data. > From 21.0.0.3 icmp_seq=2 Frag needed and DF set (mtu = 1142) > > --- 21.0.0.3 ping statistics --- > ... > > Using tcpdump, we can also see the expected ICMP FRAG_NEEDED message is not > sent into the server. > > With this patch, setting the pkt_type, we see the following: > > podman exec ovn-chassis-1 ip netns exec sw01p1 \ > ping 21.0.0.3 -M do -s 1300 -c2 > PING 21.0.0.3 (21.0.0.3) 1300(1328) bytes of data. > From 21.0.0.3 icmp_seq=1 Frag needed and DF set (mtu = 1222) > ping: local error: message too long, mtu=1222 > > --- 21.0.0.3 ping statistics --- > ... > > In this case, the first ping request receives the FRAG_NEEDED message and > a local routing exception is created. > > Tested-by: Jaime Caamano <jcaamano@redhat.com> > Reported-at: https://issues.redhat.com/browse/FDP-164 > Fixes: 58264848a5a7 ("openvswitch: Add vxlan tunneling support.") > Signed-off-by: Aaron Conole <aconole@redhat.com> Thanks for the additional comments and detailed commit message. The change looks good to me. Acked-by: Eelco Chaudron <echaudro@redhat.com>
Hello: This patch was applied to netdev/net.git (main) by Paolo Abeni <pabeni@redhat.com>: On Thu, 16 May 2024 16:09:41 -0400 you wrote: > Open vSwitch is originally intended to switch at layer 2, only dealing with > Ethernet frames. With the introduction of l3 tunnels support, it crossed > into the realm of needing to care a bit about some routing details when > making forwarding decisions. If an oversized packet would need to be > fragmented during this forwarding decision, there is a chance for pmtu > to get involved and generate a routing exception. This is gated by the > skbuff->pkt_type field. > > [...] Here is the summary with links: - [v2,net] openvswitch: Set the skbuff pkt_type for proper pmtud support. https://git.kernel.org/netdev/net/c/30a92c9e3d6b You are awesome, thank you!
diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c index 6fcd7e2ca81fe..9642255808247 100644 --- a/net/openvswitch/actions.c +++ b/net/openvswitch/actions.c @@ -936,6 +936,12 @@ static void do_output(struct datapath *dp, struct sk_buff *skb, int out_port, pskb_trim(skb, ovs_mac_header_len(key)); } + /* Need to set the pkt_type to involve the routing layer. The + * packet movement through the OVS datapath doesn't generally + * use routing, but this is needed for tunnel cases. + */ + skb->pkt_type = PACKET_OUTGOING; + if (likely(!mru || (skb->len <= mru + vport->dev->hard_header_len))) { ovs_vport_send(vport, skb, ovs_key_mac_proto(key));
Open vSwitch is originally intended to switch at layer 2, only dealing with Ethernet frames. With the introduction of l3 tunnels support, it crossed into the realm of needing to care a bit about some routing details when making forwarding decisions. If an oversized packet would need to be fragmented during this forwarding decision, there is a chance for pmtu to get involved and generate a routing exception. This is gated by the skbuff->pkt_type field. When a flow is already loaded into the openvswitch module this field is set up and transitioned properly as a packet moves from one port to another. In the case that a packet execute is invoked after a flow is newly installed this field is not properly initialized. This causes the pmtud mechanism to omit sending the required exception messages across the tunnel boundary and a second attempt needs to be made to make sure that the routing exception is properly setup. To fix this, we set the outgoing packet's pkt_type to PACKET_OUTGOING, since it can only get to the openvswitch module via a port device or packet command. Even for bridge ports as users, the pkt_type needs to be reset when doing the transmit as the packet is truly outgoing and routing needs to get involved post packet transformations, in the case of VXLAN/GENEVE/udp-tunnel packets. In general, the pkt_type on output gets ignored, since we go straight to the driver, but in the case of tunnel ports they go through IP routing layer. This issue is periodically encountered in complex setups, such as large openshift deployments, where multiple sets of tunnel traversal occurs. A way to recreate this is with the ovn-heater project that can setup a networking environment which mimics such large deployments. We need larger environments for this because we need to ensure that flow misses occur. In these environment, without this patch, we can see: ./ovn_cluster.sh start podman exec ovn-chassis-1 ip r a 170.168.0.5/32 dev eth1 mtu 1200 podman exec ovn-chassis-1 ip netns exec sw01p1 ip r flush cache podman exec ovn-chassis-1 ip netns exec sw01p1 \ ping 21.0.0.3 -M do -s 1300 -c2 PING 21.0.0.3 (21.0.0.3) 1300(1328) bytes of data. From 21.0.0.3 icmp_seq=2 Frag needed and DF set (mtu = 1142) --- 21.0.0.3 ping statistics --- ... Using tcpdump, we can also see the expected ICMP FRAG_NEEDED message is not sent into the server. With this patch, setting the pkt_type, we see the following: podman exec ovn-chassis-1 ip netns exec sw01p1 \ ping 21.0.0.3 -M do -s 1300 -c2 PING 21.0.0.3 (21.0.0.3) 1300(1328) bytes of data. From 21.0.0.3 icmp_seq=1 Frag needed and DF set (mtu = 1222) ping: local error: message too long, mtu=1222 --- 21.0.0.3 ping statistics --- ... In this case, the first ping request receives the FRAG_NEEDED message and a local routing exception is created. Tested-by: Jaime Caamano <jcaamano@redhat.com> Reported-at: https://issues.redhat.com/browse/FDP-164 Fixes: 58264848a5a7 ("openvswitch: Add vxlan tunneling support.") Signed-off-by: Aaron Conole <aconole@redhat.com> --- v1->v2: Include a comment as requested by Eelco, and add some details about bridge port packets. net/openvswitch/actions.c | 6 ++++++ 1 file changed, 6 insertions(+)