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BUG: KCSAN: data-race in ip6_mtu / rt6_disable_ip

write to 0xffff88811517f300 of 8 bytes by task 3370 on cpu 0:
 rt6_uncached_list_flush_dev net/ipv6/route.c:184 [inline]
 rt6_disable_ip+0x349/0x5f0 net/ipv6/route.c:4914
 addrconf_ifdown+0xa2/0xf20 net/ipv6/addrconf.c:3858
 addrconf_notify+0x2ff/0x950
 notifier_call_chain kernel/notifier.c:93 [inline]
 raw_notifier_call_chain+0x6f/0x1d0 kernel/notifier.c:461
 call_netdevice_notifiers_info+0xae/0x100 net/core/dev.c:1996
 call_netdevice_notifiers_extack net/core/dev.c:2034 [inline]
 call_netdevice_notifiers net/core/dev.c:2048 [inline]
 dev_close_many+0x174/0x240 net/core/dev.c:1589
 unregister_netdevice_many_notify+0x263/0x11b0 net/core/dev.c:11373
 unregister_netdevice_many+0x19/0x20 net/core/dev.c:11461
 cleanup_net+0x411/0x810 net/core/net_namespace.c:621
 process_one_work kernel/workqueue.c:3229 [inline]
 process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3310
 worker_thread+0x51d/0x6f0 kernel/workqueue.c:3391
 kthread+0x1d1/0x210 kernel/kthread.c:389
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

read to 0xffff88811517f300 of 8 bytes by task 3339 on cpu 1:
 ip6_dst_mtu_maybe_forward include/net/ip6_route.h:340 [inline]
 ip6_mtu+0x53/0x120 net/ipv6/route.c:3219
 dst_mtu include/net/dst.h:216 [inline]
 ip6_skb_dst_mtu include/net/ip6_route.h:280 [inline]
 __ip6_finish_output net/ipv6/ip6_output.c:207 [inline]
 ip6_finish_output+0x117/0x540 net/ipv6/ip6_output.c:226
 NF_HOOK_COND include/linux/netfilter.h:303 [inline]
 ip6_output+0xf5/0x230 net/ipv6/ip6_output.c:247
 dst_output include/net/dst.h:450 [inline]
 NF_HOOK include/linux/netfilter.h:314 [inline]
 mld_sendpack+0x421/0x6d0 net/ipv6/mcast.c:1819
 mld_send_cr net/ipv6/mcast.c:2120 [inline]
 mld_ifc_work+0x51a/0x7e0 net/ipv6/mcast.c:2651
 process_one_work kernel/workqueue.c:3229 [inline]
 process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3310
 worker_thread+0x51d/0x6f0 kernel/workqueue.c:3391
 kthread+0x1d1/0x210 kernel/kthread.c:389
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0xffff8881368a0000 -> 0xffff8881021c5000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3339 Comm: kworker/1:3 Tainted: G        W          6.11.0-syzkaller-05319-g4a39ac5b7d62 #0
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Workqueue: mld mld_ifc_work
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