> On Wed, 10 Aug 2016 17:35:11 -0700 (PDT) David Miller <da...@davemloft.net> > wrote: >>> commit b8247f095edd ("net: ip_finish_output_gso: If skb_gso_network_seglen >>> exceeds MTU, allow segmentation for local udp tunneled skbs") >>> >>> Given: >>> - tap0 and ovs-gre >>> - ovs-gre stacked on eth0, eth0 having the small mtu >>> >>> After encapsulation these skbs have skb_gso_network_seglen that exceed >>> eth0's ip_skb_dst_mtu. So the finnal each segment would be larger than >>> eth0 mtu. These packets maybe dropped. >>> >>> It has the same problem if tap0 bridge with ipgre or gretap device. So >>> the IPSKB_FRAG_SEGS flags should also be set in gre tunneled skbs. >>> >>> Signed-off-by: wenxu <we...@ucloud.cn> >> I am rather certain that this test is intentionally restricted to >> UDP tunnel endpoints, because GRE and other tunnel types are PMTU safe. >> >> Hannes and Shmulik? > It was restricted to UDP tun encaps per Hannes' suggestion, in order to > scope the change, as Hannes hinted gre and ipip are pmtu-safe, see [1]. > > Glancing at ip_tunnel_xmit() --> tnl_update_pmtu(), they do seem to > handle PMTU, but - if I understand correctly - only in the !skb_is_gso > case. > (since 68c3316311 "v4 GRE: Add TCP segmentation offload for GRE") > > This is probably due the same hidden assumption that 'gso_size' will be > suitable for the egress mtu even after encapsulation, which does not > hold true in some usecases as described in [2]. > > Therefore it might be that b8247f095edd needs to be augmented for > non-udp tunnels as well. > > Hannes? > > [1] http://www.spinics.net/lists/netdev/msg386447.html > [2] http://www.spinics.net/lists/netdev/msg385776.html I think non-udp tunnels should also be set And in b8247f095edd, condition skb_iif also should be removed given: ovs-internal-port bridge with ovs-gre
There is the same problem that packets from local.