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BUG: KCSAN: data-race in udp_tunnel6_xmit_skb / udp_tunnel6_xmit_skb

read-write to 0xffff88812a4451b0 of 8 bytes by task 1833 on cpu 1:
 iptunnel_xmit_stats include/net/ip_tunnels.h:461 [inline]
 ip6tunnel_xmit include/net/ip6_tunnel.h:166 [inline]
 udp_tunnel6_xmit_skb+0x43e/0x470 net/ipv6/ip6_udp_tunnel.c:109
 send6+0x2ed/0x3b0 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0xbb/0x120 drivers/net/wireguard/socket.c:178
 wg_socket_send_buffer_to_peer+0xd2/0xf0 drivers/net/wireguard/socket.c:200
 wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
 wg_packet_handshake_send_worker+0x109/0x150 drivers/net/wireguard/send.c:51
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

read-write to 0xffff88812a4451b0 of 8 bytes by task 8 on cpu 0:
 iptunnel_xmit_stats include/net/ip_tunnels.h:461 [inline]
 ip6tunnel_xmit include/net/ip6_tunnel.h:166 [inline]
 udp_tunnel6_xmit_skb+0x43e/0x470 net/ipv6/ip6_udp_tunnel.c:109
 send6+0x2ed/0x3b0 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0xbb/0x120 drivers/net/wireguard/socket.c:178
 wg_socket_send_buffer_to_peer+0xd2/0xf0 drivers/net/wireguard/socket.c:200
 wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
 wg_packet_handshake_send_worker+0x109/0x150 drivers/net/wireguard/send.c:51
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

value changed: 0x00000000000000e8 -> 0x00000000000000e9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8 Comm: kworker/u4:0 Tainted: G        W         5.18.0-rc3-syzkaller-00016-gb253435746d9-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: wg-kex-wg0 wg_packet_handshake_send_worker
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