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BUG: KCSAN: data-race in dst_cache_set_ip6 / fib6_clean_node

write to 0xffff8880233447ac of 4 bytes by task 5 on cpu 0:
 fib6_clean_node+0xc0/0x260 net/ipv6/ip6_fib.c:2176
 fib6_walk_continue+0x38e/0x430 net/ipv6/ip6_fib.c:2110
 fib6_walk net/ipv6/ip6_fib.c:2158 [inline]
 fib6_clean_tree net/ipv6/ip6_fib.c:2238 [inline]
 __fib6_clean_all+0x188/0x2b0 net/ipv6/ip6_fib.c:2254
 fib6_flush_trees+0x6c/0x80 net/ipv6/ip6_fib.c:2279
 rt_genid_bump_ipv6 include/net/net_namespace.h:452 [inline]
 addrconf_dad_completed+0x57f/0x870 net/ipv6/addrconf.c:4207
 addrconf_dad_work+0x8dd/0x1150 net/ipv6/addrconf.c:3960
 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:296

read to 0xffff8880233447ac of 4 bytes by task 9904 on cpu 1:
 fib6_get_cookie_safe include/net/ip6_fib.h:283 [inline]
 rt6_get_cookie include/net/ip6_fib.h:304 [inline]
 dst_cache_set_ip6+0xab/0x1b0 net/core/dst_cache.c:115
 send6+0x256/0x3a0 drivers/net/wireguard/socket.c:148
 wg_socket_send_skb_to_peer+0xbb/0x130 drivers/net/wireguard/socket.c:177
 wg_packet_create_data_done drivers/net/wireguard/send.c:252 [inline]
 wg_packet_tx_worker+0x1e3/0x4c0 drivers/net/wireguard/send.c:280
 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:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9904 Comm: kworker/1:6 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: wg-crypt-wg0 wg_packet_tx_worker
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