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BUG: KCSAN: data-race in fib6_clean_node / ip6_dst_check

write to 0xffff8880276a962c of 4 bytes by task 9687 on cpu 0:
 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:450 [inline]
 addrconf_dad_completed+0x57f/0x870 net/ipv6/addrconf.c:4209
 addrconf_dad_work+0x8dd/0x1160 net/ipv6/addrconf.c:3962
 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 0xffff8880276a962c of 4 bytes by task 9725 on cpu 1:
 fib6_get_cookie_safe include/net/ip6_fib.h:284 [inline]
 fib6_check net/ipv6/route.c:2561 [inline]
 rt6_dst_from_check net/ipv6/route.c:2592 [inline]
 ip6_dst_check+0x270/0x400 net/ipv6/route.c:2621
 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+0x16c/0x3b0 drivers/net/wireguard/socket.c:129
 wg_socket_send_skb_to_peer+0xbb/0x130 drivers/net/wireguard/socket.c:177
 wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
 wg_packet_tx_worker+0x142/0x360 drivers/net/wireguard/send.c:276
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9725 Comm: kworker/1:8 Not tainted 5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: wg-crypt-wg0 wg_packet_tx_worker
==================================================================
Bluetooth: hci4: command 0x041b tx timeout
Bluetooth: hci4: command 0x0419 tx timeout
usb 4-1: new high-speed USB device number 70 using dummy_hcd
usb 4-1: Using ep0 maxpacket: 32
usb 4-1: config 1 interface 0 altsetting 5 bulk endpoint 0x82 has invalid maxpacket 16
usb 4-1: config 1 interface 0 altsetting 5 bulk endpoint 0x3 has invalid maxpacket 8
usb 4-1: config 1 interface 0 has no altsetting 0
usb 4-1: New USB device found, idVendor=0525, idProduct=a4a1, bcdDevice= 0.40
usb 4-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 4-1: Product: syz
usb 4-1: Manufacturer: syz
usb 4-1: SerialNumber: syz
cdc_ether: probe of 4-1:1.0 failed with error -71
usb 4-1: USB disconnect, device number 70
usb 6-1: new high-speed USB device number 18 using dummy_hcd