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BUG: KCSAN: data-race in ip_tunnel_get_stats64 / iptunnel_xmit

write to 0xffffe8ffffc73bd0 of 8 bytes by task 12 on cpu 0:
 iptunnel_xmit_stats include/net/ip_tunnels.h:451 [inline]
 iptunnel_xmit+0x3c7/0x4b0 net/ipv4/ip_tunnel_core.c:87
 udp_tunnel_xmit_skb+0x17e/0x190 net/ipv4/udp_tunnel_core.c:190
 send4+0x399/0x550 drivers/net/wireguard/socket.c:85
 wg_socket_send_skb_to_peer+0x92/0x130 drivers/net/wireguard/socket.c:174
 wg_packet_create_data_done drivers/net/wireguard/send.c:252 [inline]
 wg_packet_tx_worker+0x1e2/0x4c0 drivers/net/wireguard/send.c:280
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffffe8ffffc73bd0 of 8 bytes by task 8746 on cpu 1:
 ip_tunnel_get_stats64+0xd1/0x1c0 net/ipv4/ip_tunnel_core.c:449
 dev_get_stats+0x65/0x180 net/core/dev.c:10239
 rtnl_fill_stats+0x45/0x320 net/core/rtnetlink.c:1209
 rtnl_fill_ifinfo+0xe92/0x2430 net/core/rtnetlink.c:1781
 rtmsg_ifinfo_build_skb+0xa8/0x130 net/core/rtnetlink.c:3808
 rtmsg_ifinfo_event net/core/rtnetlink.c:3840 [inline]
 rtmsg_ifinfo+0x58/0xc0 net/core/rtnetlink.c:3849
 __dev_notify_flags+0x63/0x390 net/core/dev.c:8382
 dev_change_flags+0xa2/0xc0 net/core/dev.c:8424
 do_setlink+0x736/0x2220 net/core/rtnetlink.c:2706
 __rtnl_newlink net/core/rtnetlink.c:3374 [inline]
 rtnl_newlink+0xe62/0x1340 net/core/rtnetlink.c:3500
 rtnetlink_rcv_msg+0x71b/0x7b0 net/core/rtnetlink.c:5563
 netlink_rcv_skb+0x13e/0x240 net/netlink/af_netlink.c:2470
 rtnetlink_rcv+0x18/0x20 net/core/rtnetlink.c:5581
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x5e2/0x6b0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x6d8/0x7a0 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg net/socket.c:671 [inline]
 __sys_sendto+0x2ae/0x380 net/socket.c:1992
 __do_sys_sendto net/socket.c:2004 [inline]
 __se_sys_sendto net/socket.c:2000 [inline]
 __x64_sys_sendto+0x74/0x90 net/socket.c:2000
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8746 Comm: syz-executor.4 Not tainted 5.9.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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