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BUG: KCSAN: data-race in dev_get_tstats64 / iptunnel_xmit

write to 0xffffe8ffffd536f8 of 8 bytes by task 1964 on cpu 1:
 iptunnel_xmit_stats include/net/ip_tunnels.h:448 [inline]
 iptunnel_xmit+0x399/0x4a0 net/ipv4/ip_tunnel_core.c:87
 udp_tunnel_xmit_skb+0x16f/0x180 net/ipv4/udp_tunnel_core.c:174
 send4+0x4f0/0x530 drivers/net/wireguard/socket.c:85
 wg_socket_send_skb_to_peer drivers/net/wireguard/socket.c:174 [inline]
 wg_socket_send_buffer_to_peer+0x15b/0x210 drivers/net/wireguard/socket.c:199
 wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
 wg_packet_handshake_send_worker+0xfa/0x140 drivers/net/wireguard/send.c:51
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffffe8ffffd536f8 of 8 bytes by task 8407 on cpu 0:
 dev_fetch_sw_netstats net/core/dev.c:10561 [inline]
 dev_get_tstats64+0x109/0x1d0 net/core/dev.c:10583
 dev_get_stats+0x65/0x180 net/core/dev.c:10525
 rtnl_fill_stats+0x45/0x320 net/core/rtnetlink.c:1211
 rtnl_fill_ifinfo+0xe98/0x2440 net/core/rtnetlink.c:1783
 rtmsg_ifinfo_build_skb+0xa8/0x130 net/core/rtnetlink.c:3798
 rtmsg_ifinfo_event net/core/rtnetlink.c:3830 [inline]
 rtmsg_ifinfo+0x58/0xc0 net/core/rtnetlink.c:3839
 __dev_notify_flags+0x63/0x3a0 net/core/dev.c:8691
 dev_change_flags+0xa2/0xc0 net/core/dev.c:8733
 do_setlink+0x746/0x2280 net/core/rtnetlink.c:2708
 __rtnl_newlink net/core/rtnetlink.c:3376 [inline]
 rtnl_newlink+0xe7e/0x1310 net/core/rtnetlink.c:3491
 rtnetlink_rcv_msg+0x728/0x7c0 net/core/rtnetlink.c:5553
 netlink_rcv_skb+0x13e/0x240 net/netlink/af_netlink.c:2502
 rtnetlink_rcv+0x18/0x20 net/core/rtnetlink.c:5571
 netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
 netlink_unicast+0x5fc/0x6c0 net/netlink/af_netlink.c:1338
 netlink_sendmsg+0x6f8/0x7c0 net/netlink/af_netlink.c:1927
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg net/socket.c:674 [inline]
 __sys_sendto+0x2a8/0x370 net/socket.c:1977
 __do_sys_sendto net/socket.c:1989 [inline]
 __se_sys_sendto net/socket.c:1985 [inline]
 __x64_sys_sendto+0x74/0x90 net/socket.c:1985
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8407 Comm: syz-executor.0 Not tainted 5.12.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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