I'm also experiencing this crash.  I would be glad to provide any info.

I tested with your kernel without seeing any obvious difference in behavior.  machine is an old dell 1950 with bnx2 onboard  and a bnx2 add-in pcie card.  i'm not sure but i think its exploding when a packet comes from external to a tenant VM via GRE tunnels.  This would be receive on eth3 and send out on eth1.  i've included ethtool output below.


openstack-neutron:/root# uname -a
Linux openstack-neutron.stanford.edu 3.13.11-031311-generic #201404222035 SMP Wed Apr 23 00:36:02 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux



openstack-neutron login: [  236.982433] ------------[ cut here ]------------
[  236.986375] kernel BUG at /home/apw/COD/linux/net/core/skbuff.c:2903!

[  236.996021] invalid opcode: 0000 [#1] SMP 
[  236.996021] Modules linked in: xt_nat xt_conntrack ip6table_filter ip6_tables iptable_filter xt_REDIRECT xt__
[  236.996021] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.13.11-031311-generic #201404222035
[  236.996021] Hardware name: Dell Inc. PowerEdge 1950/0TT740, BIOS 2.5.0 09/12/2008
[  236.996021] task: ffff8802341b97f0 ti: ffff8802341b4000 task.ti: ffff8802341b4000
[  236.996021] RIP: 0010:[<ffffffff8162de14>]  [<ffffffff8162de14>] skb_segment+0x8a4/0x8c0
[  236.996021] RSP: 0018:ffff88023fc432e8  EFLAGS: 00010202
[  236.996021] RAX: 0000000000000000 RBX: ffff880232dcba00 RCX: 0000000000000050
[  236.996021] RDX: ffff88022f88c4f0 RSI: ffff88022f88c400 RDI: ffff880232dcab00
[  236.996021] RBP: ffff88023fc433b8 R08: 0000000000000042 R09: 0000000000000050
[  236.996021] R10: 00000000000005b8 R11: 0000000000000000 R12: ffff88022f88c8f0
[  236.996021] R13: 0000000000000000 R14: ffff880232dcb200 R15: ffff880232dcab00
[  236.996021] FS:  0000000000000000(0000) GS:ffff88023fc40000(0000) knlGS:0000000000000000
[  236.996021] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  236.996021] CR2: 0000000001c7c170 CR3: 0000000232eec000 CR4: 00000000000007e0
[  236.996021] Stack:
[  236.996021]  0000000000000000 0000000000000000 0000000000000000 ffff88022f88c894
[  236.996021]  ffff88022f88c400 000000000000000e 00000000000005b8 0000000100000000
[  236.996021]  0000000000000000 ffffffffffffffbe ffffffffffffffd6 000000000000006c
[  236.996021] Call Trace:
[  236.996021]  <IRQ> 
[  236.996021]  [<ffffffff8169b6da>] tcp_gso_segment.part.7+0x11a/0x3c0
[  236.996021]  [<ffffffff8169b9b1>] tcp_gso_segment+0x31/0x60
[  236.996021]  [<ffffffff816ab5c5>] inet_gso_segment+0x135/0x370
[  236.996021]  [<ffffffff8163c5fe>] skb_mac_gso_segment+0xae/0x180
[  236.996021]  [<ffffffffa0085930>] gre_gso_segment+0x130/0x370 [gre]
[  236.996021]  [<ffffffff816ab5c5>] inet_gso_segment+0x135/0x370
[  236.996021]  [<ffffffff8163c5fe>] skb_mac_gso_segment+0xae/0x180
[  236.996021]  [<ffffffff8163c72e>] __skb_gso_segment+0x5e/0xc0
[  236.996021]  [<ffffffff8163c919>] dev_hard_start_xmit+0x189/0x5a0
[  236.996021]  [<ffffffff8165bfce>] sch_direct_xmit+0xfe/0x1d0
[  236.996021]  [<ffffffff8163cea8>] __dev_queue_xmit+0x178/0x4b0
[  236.996021]  [<ffffffff81677080>] ? __ip_append_data.isra.40+0x9d0/0x9d0
[  236.996021]  [<ffffffff8163d200>] dev_queue_xmit+0x10/0x20
[  236.996021]  [<ffffffff816772a4>] ip_finish_output+0x224/0x3f0
[  236.996021]  [<ffffffff81677da8>] ip_output+0x58/0x90
[  236.996021]  [<ffffffff81677519>] ip_local_out+0x29/0x30
[  236.996021]  [<ffffffff816bb098>] iptunnel_xmit+0xf8/0x120
[  236.996021]  [<ffffffffa0375d78>] gre_tnl_send+0x298/0x370 [openvswitch]
[  236.996021]  [<ffffffffa0373ab9>] ? find_bucket.isra.3+0x69/0x70 [openvswitch]
[  236.996021]  [<ffffffffa0373c91>] ? masked_flow_lookup+0x71/0x140 [openvswitch]
[  236.996021]  [<ffffffffa0374c32>] ovs_vport_send+0x22/0x80 [openvswitch]
[  236.996021]  [<ffffffff8163a063>] ? netif_rx.part.79+0x43/0x110
[  236.996021]  [<ffffffffa036b3de>] do_output+0x2e/0x50 [openvswitch]
[  236.996021]  [<ffffffffa036c045>] do_execute_actions+0x1b5/0x220 [openvswitch]
[  236.996021]  [<ffffffffa0374286>] ? ovs_flow_tbl_lookup+0x76/0x90 [openvswitch]
[  236.996021]  [<ffffffffa036c0db>] ovs_execute_actions+0x2b/0x30 [openvswitch]
[  236.996021]  [<ffffffffa036e8ad>] ovs_dp_process_received_packet+0x9d/0x130 [openvswitch]
[  236.996021]  [<ffffffffa0374b8a>] ovs_vport_receive+0x2a/0x30 [openvswitch]
[  236.996021]  [<ffffffffa037507d>] internal_dev_xmit+0x1d/0x30 [openvswitch]
[  236.996021]  [<ffffffff8163caa2>] dev_hard_start_xmit+0x312/0x5a0
[  236.996021]  [<ffffffff8163cffc>] __dev_queue_xmit+0x2cc/0x4b0
[  236.996021]  [<ffffffffa0397706>] ? ipv4_confirm+0x76/0xf0 [nf_conntrack_ipv4]
[  236.996021]  [<ffffffff8163d200>] dev_queue_xmit+0x10/0x20
[  236.996021]  [<ffffffff81645573>] neigh_resolve_output+0x123/0x220
[  236.996021]  [<ffffffff81677080>] ? __ip_append_data.isra.40+0x9d0/0x9d0
[  236.996021]  [<ffffffff8167730d>] ip_finish_output+0x28d/0x3f0
[  236.996021]  [<ffffffff81677da8>] ip_output+0x58/0x90
[  236.996021]  [<ffffffff81673c99>] ip_forward_finish+0x89/0x180
[  236.996021]  [<ffffffff81674089>] ip_forward+0x2f9/0x3f0
[  236.996021]  [<ffffffff81671e61>] ip_rcv_finish+0x121/0x380
[  236.996021]  [<ffffffff81672736>] ip_rcv+0x286/0x380
[  236.996021]  [<ffffffff8163a881>] ? __netif_receive_skb+0x21/0x70
[  236.996021]  [<ffffffff8163a712>] __netif_receive_skb_core+0x5e2/0x730
[  236.996021]  [<ffffffff8163a881>] __netif_receive_skb+0x21/0x70
[  236.996021]  [<ffffffff8163b141>] process_backlog+0xb1/0x190
[  236.996021]  [<ffffffff8163b979>] net_rx_action+0x139/0x250
[  236.996021]  [<ffffffff8106eccd>] __do_softirq+0xdd/0x300
[  236.996021]  [<ffffffff8106f28e>] irq_exit+0x11e/0x140
[  236.996021]  [<ffffffff81758923>] do_IRQ+0x63/0xe0
[  236.996021]  [<ffffffff8174daed>] common_interrupt+0x6d/0x6d
[  236.996021]  <EOI> 
[  236.996021]  [<ffffffff81091e38>] ? hrtimer_start+0x18/0x20
[  236.996021]  [<ffffffff81052796>] ? native_safe_halt+0x6/0x10
[  236.996021]  [<ffffffff8101dca3>] default_idle+0x23/0xe0
[  236.996021]  [<ffffffff8101e526>] arch_cpu_idle+0x26/0x30
[  236.996021]  [<ffffffff810c2628>] cpu_idle_loop+0x78/0x270
[  236.996021]  [<ffffffff810c288b>] cpu_startup_entry+0x6b/0x70
[  236.996021]  [<ffffffff81044188>] start_secondary+0xc8/0xd0
[  236.996021] Code: c0 44 8b 8d 50 ff ff ff 0f 84 e3 fe ff ff 8b 55 a8 44 89 ce 48 c7 c7 48 9b b0 81 31 c0 e8 5
[  236.996021] RIP  [<ffffffff8162de14>] skb_segment+0x8a4/0x8c0
[  236.996021]  RSP <ffff88023fc432e8>
[  238.265527] ---[ end trace 4af2fd01f646443f ]---
[  238.268045] Kernel panic - not syncing: Fatal exception in interrupt
[  238.268045] drm_kms_helper: panic occurred, switching back to text console


openstack-neutron:/root# ethtool -k eth3
Features for eth3:
rx-checksumming: on
tx-checksumming: on
	tx-checksum-ipv4: on
	tx-checksum-ip-generic: off [fixed]
	tx-checksum-ipv6: on
	tx-checksum-fcoe-crc: off [fixed]
	tx-checksum-sctp: off [fixed]
scatter-gather: on
	tx-scatter-gather: on
	tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
	tx-tcp-segmentation: on
	tx-tcp-ecn-segmentation: on
	tx-tcp6-segmentation: on
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: on
highdma: on [fixed]
rx-vlan-filter: off [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-ipip-segmentation: off [fixed]
tx-sit-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
tx-mpls-segmentation: off [fixed]
fcoe-mtu: off [fixed]
tx-nocache-copy: on
loopback: off [fixed]
rx-fcs: off [fixed]
rx-all: off [fixed]
tx-vlan-stag-hw-insert: off [fixed]
rx-vlan-stag-hw-parse: off [fixed]
rx-vlan-stag-filter: off [fixed]
l2-fwd-offload: off [fixed]


openstack-neutron:/root# ethtool -k eth1
Features for eth1:
rx-checksumming: on
tx-checksumming: on
	tx-checksum-ipv4: on
	tx-checksum-ip-generic: off [fixed]
	tx-checksum-ipv6: off [fixed]
	tx-checksum-fcoe-crc: off [fixed]
	tx-checksum-sctp: off [fixed]
scatter-gather: on
	tx-scatter-gather: on
	tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
	tx-tcp-segmentation: on
	tx-tcp-ecn-segmentation: on
	tx-tcp6-segmentation: off [fixed]
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: on
highdma: on [fixed]
rx-vlan-filter: off [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-ipip-segmentation: off [fixed]
tx-sit-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
tx-mpls-segmentation: off [fixed]
fcoe-mtu: off [fixed]
tx-nocache-copy: on
loopback: off [fixed]
rx-fcs: off [fixed]
rx-all: off [fixed]
tx-vlan-stag-hw-insert: off [fixed]
rx-vlan-stag-hw-parse: off [fixed]
rx-vlan-stag-filter: off [fixed]
l2-fwd-offload: off [fixed]