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BUG: KCSAN: data-race in ip_tunnel_get_stats64 / iptunnel_xmit

write to 0xffffe8ffffc4dd90 of 8 bytes by task 12 on cpu 0:
 iptunnel_xmit_stats include/net/ip_tunnels.h:446 [inline]
 iptunnel_xmit+0x3c7/0x4b0 net/ipv4/ip_tunnel_core.c:86
 udp_tunnel_xmit_skb+0x17e/0x190 net/ipv4/udp_tunnel.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+0x3cb/0x990 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x210/0x220 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffffe8ffffc4dd90 of 8 bytes by task 8663 on cpu 1:
 ip_tunnel_get_stats64+0xd1/0x1c0 net/ipv4/ip_tunnel_core.c:204
 dev_get_stats+0x65/0x180 net/core/dev.c:9847
 rtnl_fill_stats+0x45/0x320 net/core/rtnetlink.c:1199
 rtnl_fill_ifinfo+0xd4d/0x2340 net/core/rtnetlink.c:1741
 rtmsg_ifinfo_build_skb+0xa8/0x130 net/core/rtnetlink.c:3705
 rtmsg_ifinfo_event net/core/rtnetlink.c:3737 [inline]
 rtmsg_ifinfo+0x58/0xc0 net/core/rtnetlink.c:3746
 __dev_notify_flags+0x63/0x390 net/core/dev.c:8312
 dev_change_flags+0xa2/0xc0 net/core/dev.c:8354
 do_setlink+0x77a/0x2080 net/core/rtnetlink.c:2604
 __rtnl_newlink net/core/rtnetlink.c:3272 [inline]
 rtnl_newlink+0xe6c/0x1320 net/core/rtnetlink.c:3397
 rtnetlink_rcv_msg+0x71b/0x7b0 net/core/rtnetlink.c:5460
 netlink_rcv_skb+0x13e/0x240 net/netlink/af_netlink.c:2469
 rtnetlink_rcv+0x18/0x20 net/core/rtnetlink.c:5478
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x5e2/0x6b0 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x6d8/0x7a0 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 __sys_sendto+0x2ad/0x380 net/socket.c:1995
 __do_sys_sendto net/socket.c:2007 [inline]
 __se_sys_sendto net/socket.c:2003 [inline]
 __x64_sys_sendto+0x74/0x90 net/socket.c:2003
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8663 Comm: syz-executor.0 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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