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BUG: KCSAN: data-race in fib6_clean_node / ip6_dst_check

write to 0xffff8880268d852c of 4 bytes by task 9231 on cpu 1:
 fib6_clean_node+0xc0/0x260 net/ipv6/ip6_fib.c:2177
 fib6_walk_continue+0x38e/0x430 net/ipv6/ip6_fib.c:2111
 fib6_walk net/ipv6/ip6_fib.c:2159 [inline]
 fib6_clean_tree net/ipv6/ip6_fib.c:2239 [inline]
 __fib6_clean_all+0x188/0x2b0 net/ipv6/ip6_fib.c:2255
 fib6_flush_trees+0x6c/0x80 net/ipv6/ip6_fib.c:2280
 rt_genid_bump_ipv6 include/net/net_namespace.h:458 [inline]
 addrconf_dad_completed+0x57f/0x860 net/ipv6/addrconf.c:4205
 addrconf_dad_work+0x8dd/0x1150 net/ipv6/addrconf.c:3958
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
 worker_thread+0x635/0xb90 kernel/workqueue.c:2418
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff8880268d852c of 4 bytes by task 5 on cpu 0:
 fib6_get_cookie_safe include/net/ip6_fib.h:283 [inline]
 fib6_check net/ipv6/route.c:2577 [inline]
 rt6_dst_from_check net/ipv6/route.c:2608 [inline]
 ip6_dst_check+0x270/0x400 net/ipv6/route.c:2636
 dst_cache_per_cpu_get+0x103/0x1b0 net/core/dst_cache.c:50
 dst_cache_get_ip6+0x33/0x70 net/core/dst_cache.c:130
 send6+0x168/0x3a0 drivers/net/wireguard/socket.c:129
 wg_socket_send_skb_to_peer+0xbb/0x120 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:2272
 worker_thread+0x635/0xb90 kernel/workqueue.c:2418
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.10.0-rc6-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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