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BUG: KCSAN: data-race in __neigh_event_send / neigh_resolve_output

write to 0xffff8880a1387a85 of 1 bytes by task 21 on cpu 1:
 __neigh_event_send+0x403/0xb10 net/core/neighbour.c:1126
 neigh_event_send include/net/neighbour.h:443 [inline]
 neigh_resolve_output+0x104/0x400 net/core/neighbour.c:1473
 neigh_output include/net/neighbour.h:509 [inline]
 ip_finish_output2+0x4e2/0xb60 net/ipv4/ip_output.c:228
 __ip_finish_output+0x395/0x3e0 net/ipv4/ip_output.c:306
 ip_finish_output+0x39/0x160 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:296 [inline]
 ip_output+0xf6/0x1a0 net/ipv4/ip_output.c:430
 dst_output include/net/dst.h:435 [inline]
 ip_local_out+0x60/0x80 net/ipv4/ip_output.c:125
 iptunnel_xmit+0x30d/0x4b0 net/ipv4/ip_tunnel_core.c:81
 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 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+0xf9/0x140 drivers/net/wireguard/send.c:51
 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 0xffff8880a1387a85 of 1 bytes by task 30 on cpu 0:
 neigh_event_send include/net/neighbour.h:442 [inline]
 neigh_resolve_output+0x6f/0x400 net/core/neighbour.c:1473
 neigh_output include/net/neighbour.h:509 [inline]
 ip_finish_output2+0x4e2/0xb60 net/ipv4/ip_output.c:228
 __ip_finish_output+0x395/0x3e0 net/ipv4/ip_output.c:306
 ip_finish_output+0x39/0x160 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:296 [inline]
 ip_output+0xf6/0x1a0 net/ipv4/ip_output.c:430
 dst_output include/net/dst.h:435 [inline]
 ip_local_out+0x60/0x80 net/ipv4/ip_output.c:125
 iptunnel_xmit+0x30d/0x4b0 net/ipv4/ip_tunnel_core.c:81
 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 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+0xf9/0x140 drivers/net/wireguard/send.c:51
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30 Comm: kworker/u4:2 Not tainted 5.8.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: wg-kex-wg1 wg_packet_handshake_send_worker
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