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BUG: KCSAN: data-race in udp_tunnel6_xmit_skb / udp_tunnel6_xmit_skb

read-write to 0xffff8881392a7160 of 8 bytes by task 15884 on cpu 0:
 iptunnel_xmit_stats include/net/ip_tunnels.h:480 [inline]
 ip6tunnel_xmit include/net/ip6_tunnel.h:166 [inline]
 udp_tunnel6_xmit_skb+0x44d/0x4c0 net/ipv6/ip6_udp_tunnel.c:109
 send6+0x2ea/0x3a0 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0xbd/0x130 drivers/net/wireguard/socket.c:178
 wg_socket_send_buffer_to_peer+0xd6/0x100 drivers/net/wireguard/socket.c:200
 wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
 wg_packet_handshake_send_worker+0x10c/0x150 drivers/net/wireguard/send.c:51
 process_one_work+0x3e6/0x750 kernel/workqueue.c:2390
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2537
 kthread+0x1ac/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

read-write to 0xffff8881392a7160 of 8 bytes by task 22539 on cpu 1:
 iptunnel_xmit_stats include/net/ip_tunnels.h:480 [inline]
 ip6tunnel_xmit include/net/ip6_tunnel.h:166 [inline]
 udp_tunnel6_xmit_skb+0x44d/0x4c0 net/ipv6/ip6_udp_tunnel.c:109
 send6+0x2ea/0x3a0 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0xbd/0x130 drivers/net/wireguard/socket.c:178
 wg_socket_send_buffer_to_peer+0xd6/0x100 drivers/net/wireguard/socket.c:200
 wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
 wg_packet_handshake_send_worker+0x10c/0x150 drivers/net/wireguard/send.c:51
 process_one_work+0x3e6/0x750 kernel/workqueue.c:2390
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2537
 kthread+0x1ac/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

value changed: 0x00000000000002c9 -> 0x00000000000002ca

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22539 Comm: kworker/u4:3 Not tainted 6.3.0-rc4-syzkaller-00025-g3a93e40326c8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Workqueue: wg-kex-wg0 wg_packet_handshake_send_worker
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