The crash is occur on Centos 6.4, when we use gre vport of openvswitch!

<1>BUG: unable to handle kernel NULL pointer dereference at (null)
<1>IP: [<(null)>] (null)
<4>PGD c2910b067 PUD c2927d067 PMD 0 
<4>Oops: 0010 [#1] SMP 
<4>last sysfs file: /sys/devices/virtual/net/gretap0/flags
<4>CPU 20 
<4>Modules linked in: ip_gre ip_tunnel xt_conntrack act_police cls_basic sch_ingress veth ipt_REDIRECT ipmi_devintf ipv6 openvswitch vxlan iptable_filter iptable_nat nf_nat nf_conntrack_ipv4 nf_conntrack nf_defrag_ipv4 iptable_mangle iptable_raw iptable_security ip_tables power_meter sg dcdbas microcode sb_edac edac_core iTCO_wdt iTCO_vendor_support shpchp tg3 ext4 jbd2 mbcache sd_mod crc_t10dif ahci wmi megaraid_sas dm_mirror dm_region_hash dm_log dm_mod [last unloaded: speedstep_lib]
<4>
<4>Pid: 2358, comm: ovs-vswitchd Not tainted 2.6.32-358.123.2.openstack.el6.x86_64 #1 Dell Inc. PowerEdge R620/0D2D5F
<4>RIP: 0010:[<0000000000000000>]  [<(null)>] (null)
<4>RSP: 0018:ffff880053743c70  EFLAGS: 00010282
<4>RAX: ffffffffa01cbe20 RBX: ffff880bda46ecc0 RCX: 0000000000000000
<4>RDX: ffff880053743c78 RSI: 0000000000000000 RDI: ffff880bda46ecc0
<4>RBP: ffff880053743ca8 R08: 000000005617f772 R09: 0000000000000000
<4>R10: 0000000000000000 R11: 0000000000000000 R12: ffff880053743c78
<4>R13: 0000000000000000 R14: ffff880be5a5b244 R15: 0000000000000000
<4>FS:  00007fe5d5f837c0(0000) GS:ffff880053740000(0000) knlGS:0000000000000000
<4>CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4>CR2: 0000000000000000 CR3: 0000000c2a804000 CR4: 00000000000407e0
<4>DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
<4>DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
<4>Process ovs-vswitchd (pid: 2358, threadinfo ffff880c284e0000, task ffff880c28d1f500)
<4>Stack:
<4> ffffffff814c6e61 00000000aba73000 0000000000000000 ffff880053743cc8
<4><d> 000000000000002f ffff880bda46ecc0 ffff881800deb200 ffff880053743cb8
<4><d> ffffffff814c676b ffff880053743cf8 ffffffff814afa91 ffff880053743ce8
<4>Call Trace:
<4> <IRQ> 
<4> [<ffffffff814c6e61>] ? gre_cisco_err+0x71/0x80
<4> [<ffffffff814c676b>] gre_err+0x4b/0x50
<4> [<ffffffff814afa91>] icmp_unreach+0x141/0x2e0
<4> [<ffffffff814b02e0>] icmp_rcv+0x290/0x330
<4> [<ffffffff814a8c71>] ? raw_local_deliver+0x221/0x250
<4> [<ffffffff8148222d>] ip_local_deliver_finish+0xdd/0x2d0
<4> [<ffffffff814824b8>] ip_local_deliver+0x98/0xa0
<4> [<ffffffff8148197d>] ip_rcv_finish+0x12d/0x440
<4> [<ffffffff81481f05>] ip_rcv+0x275/0x350
<4> [<ffffffffa01ca503>] ? ovs_netdev_frame_hook+0xb3/0x110 [openvswitch]
<4> [<ffffffff81449e6b>] __netif_receive_skb+0x4ab/0x750
<4> [<ffffffff8144a1aa>] process_backlog+0x9a/0x100
<4> [<ffffffff8144f483>] net_rx_action+0x103/0x2f0
<4> [<ffffffff810770b1>] __do_softirq+0xc1/0x1e0
<4> [<ffffffff8100c1cc>] ? call_softirq+0x1c/0x30
<4> [<ffffffff8100c1cc>] call_softirq+0x1c/0x30
<4> <EOI> 
<4> [<ffffffff8100de05>] ? do_softirq+0x65/0xa0
<4> [<ffffffff81076f3a>] local_bh_enable+0x9a/0xb0
<4> [<ffffffffa01c3b9c>] ovs_packet_cmd_execute+0x20c/0x240 [openvswitch]
<4> [<ffffffff81476013>] genl_rcv_msg+0x203/0x250
<4> [<ffffffff81475e10>] ? genl_rcv_msg+0x0/0x250
<4> [<ffffffff81474ca9>] netlink_rcv_skb+0xa9/0xd0
<4> [<ffffffff81475df5>] genl_rcv+0x25/0x40
<4> [<ffffffff814748db>] netlink_unicast+0x2db/0x320
<4> [<ffffffff81475350>] netlink_sendmsg+0x2c0/0x3d0
<4> [<ffffffff81436b33>] sock_sendmsg+0x123/0x150
<4> [<ffffffff814387e3>] ? sock_recvmsg+0x133/0x160
<4> [<ffffffff81096da0>] ? autoremove_wake_function+0x0/0x40
<4> [<ffffffff81197af0>] ? pollwake+0x0/0x60
<4> [<ffffffff81197af0>] ? pollwake+0x0/0x60
<4> [<ffffffff8118c687>] ? pipe_read+0x2a7/0x4e0
<4> [<ffffffff81197af0>] ? pollwake+0x0/0x60
<4> [<ffffffff81438326>] __sys_sendmsg+0x406/0x420
<4> [<ffffffff811c7c54>] ? ep_scan_ready_list+0x194/0x1a0
<4> [<ffffffff811c7dae>] ? ep_poll+0x12e/0x330
<4> [<ffffffff8121cb26>] ? security_file_permission+0x16/0x20
<4> [<ffffffff81438549>] sys_sendmsg+0x49/0x90
<4> [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
<4>Code:  Bad RIP value.
<1>RIP  [<(null)>] (null)
<4> RSP <ffff880053743c70>
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