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BUG: KCSAN: data-race in pcpu_alloc / pcpu_free_area

read-write to 0xffffffff8840c49c of 4 bytes by task 6949 on cpu 1:
 pcpu_update_empty_pages mm/percpu.c:602 [inline]
 pcpu_block_update_hint_free mm/percpu.c:1044 [inline]
 pcpu_free_area+0x4e2/0x570 mm/percpu.c:1302
 free_percpu+0x1c6/0xb30 mm/percpu.c:2303
 xt_percpu_counter_free+0x63/0x80 net/netfilter/x_tables.c:1951
 cleanup_entry+0x186/0x1b0 net/ipv4/netfilter/ip_tables.c:654
 __ipt_unregister_table net/ipv4/netfilter/ip_tables.c:1717 [inline]
 ipt_unregister_table_exit+0x77/0x110 net/ipv4/netfilter/ip_tables.c:1805
 iptable_filter_net_exit+0x1c/0x30 net/ipv4/netfilter/iptable_filter.c:69
 ops_exit_list net/core/net_namespace.c:173 [inline]
 cleanup_net+0x47b/0x830 net/core/net_namespace.c:640
 process_one_work kernel/workqueue.c:3267 [inline]
 process_scheduled_works+0x465/0x990 kernel/workqueue.c:3348
 worker_thread+0x526/0x730 kernel/workqueue.c:3429
 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 0xffffffff8840c49c of 4 bytes by task 26203 on cpu 0:
 pcpu_alloc+0x9aa/0x10d0 mm/percpu.c:1868
 __alloc_percpu_gfp+0x26/0x30 mm/percpu.c:1930
 fib6_nh_init+0x60b/0x15c0 net/ipv6/route.c:3626
 ip6_route_info_create+0x7b7/0xba0 net/ipv6/route.c:3807
 addrconf_f6i_alloc+0x188/0x280 net/ipv6/route.c:4583
 fixup_permanent_addr net/ipv6/addrconf.c:3584 [inline]
 addrconf_permanent_addr+0x13c/0x5e0 net/ipv6/addrconf.c:3623
 addrconf_notify+0x681/0x950 net/ipv6/addrconf.c:3695
 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:1950
 __dev_notify_flags+0xff/0x1a0
 dev_change_flags+0xab/0xd0 net/core/dev.c:8769
 do_setlink+0x841/0x2490 net/core/rtnetlink.c:2884
 __rtnl_newlink net/core/rtnetlink.c:3680 [inline]
 rtnl_newlink+0x11a1/0x1690 net/core/rtnetlink.c:3727
 rtnetlink_rcv_msg+0x82e/0x8e0 net/core/rtnetlink.c:6595
 netlink_rcv_skb+0x12c/0x230 net/netlink/af_netlink.c:2559
 rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:6613
 netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
 netlink_unicast+0x58d/0x660 net/netlink/af_netlink.c:1361
 netlink_sendmsg+0x5d3/0x6e0 net/netlink/af_netlink.c:1905
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg+0x140/0x180 net/socket.c:745
 __sys_sendto+0x1e5/0x260 net/socket.c:2191
 __do_sys_sendto net/socket.c:2203 [inline]
 __se_sys_sendto net/socket.c:2199 [inline]
 __x64_sys_sendto+0x78/0x90 net/socket.c:2199
 x64_sys_call+0x16bb/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000065 -> 0x00000066

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 26203 Comm: syz-executor.0 Not tainted 6.9.0-syzkaller-03117-gb850dc206a57 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
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