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BUG: KCSAN: data-race in pcpu_alloc / pcpu_chunk_populated

write to 0xffffffff88afae40 of 4 bytes by task 8922 on cpu 1:
 pcpu_update_empty_pages mm/percpu.c:548 [inline]
 pcpu_chunk_populated+0xe2/0x100 mm/percpu.c:1454
 pcpu_alloc+0x984/0xd00 mm/percpu.c:1693
 __alloc_percpu+0x2a/0x40 mm/percpu.c:1767
 xt_percpu_counter_alloc+0xfb/0x120 net/netfilter/x_tables.c:1842
 find_check_entry.isra.0+0x60/0x540 net/ipv4/netfilter/ip_tables.c:527
 translate_table+0x72a/0xb80 net/ipv4/netfilter/ip_tables.c:717
 ipt_register_table+0xba/0x200 net/ipv4/netfilter/ip_tables.c:1772
 iptable_nat_table_init.part.0+0x60/0x180 net/ipv4/netfilter/iptable_nat.c:99
 iptable_nat_table_init+0x4c/0x60 net/ipv4/netfilter/iptable_nat.c:114
 xt_find_table_lock+0x222/0x300 net/netfilter/x_tables.c:1223
 xt_request_find_table_lock+0x31/0xc0 net/netfilter/x_tables.c:1253
 get_info+0xda/0x460 net/ipv6/netfilter/ip6_tables.c:981
 do_ipt_get_ctl+0xbf/0x640 net/ipv4/netfilter/ip_tables.c:1696
 nf_sockopt net/netfilter/nf_sockopt.c:104 [inline]
 nf_getsockopt+0x6a/0xa0 net/netfilter/nf_sockopt.c:122
 ip_getsockopt net/ipv4/ip_sockglue.c:1576 [inline]
 ip_getsockopt+0x119/0x160 net/ipv4/ip_sockglue.c:1556
 tcp_getsockopt net/ipv4/tcp.c:3726 [inline]
 tcp_getsockopt+0x6c/0xb0 net/ipv4/tcp.c:3720
 sock_common_getsockopt+0x5d/0x80 net/core/sock.c:3131
 __sys_getsockopt+0xed/0x210 net/socket.c:2177
 __do_sys_getsockopt net/socket.c:2192 [inline]
 __se_sys_getsockopt net/socket.c:2189 [inline]
 __x64_sys_getsockopt+0x6b/0x80 net/socket.c:2189
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff88afae40 of 4 bytes by task 9411 on cpu 0:
 pcpu_alloc+0x3c2/0xd00 mm/percpu.c:1700
 __alloc_percpu_gfp+0x2d/0x40 mm/percpu.c:1754
 fib6_nh_init+0x306/0x1090 net/ipv6/route.c:3480
 ip6_route_info_create+0x99d/0xe20 net/ipv6/route.c:3661
 ip6_route_add+0x2c/0x100 net/ipv6/route.c:3701
 addrconf_prefix_route.isra.0+0x1e3/0x260 net/ipv6/addrconf.c:2400
 fixup_permanent_addr net/ipv6/addrconf.c:3451 [inline]
 addrconf_permanent_addr net/ipv6/addrconf.c:3475 [inline]
 addrconf_notify+0xff0/0x1550 net/ipv6/addrconf.c:3543
 notifier_call_chain+0xda/0x160 kernel/notifier.c:83
 __raw_notifier_call_chain kernel/notifier.c:361 [inline]
 raw_notifier_call_chain+0x33/0x50 kernel/notifier.c:368
 call_netdevice_notifiers_info net/core/dev.c:1948 [inline]
 call_netdevice_notifiers_info+0x96/0x110 net/core/dev.c:1933
 call_netdevice_notifiers_extack net/core/dev.c:1960 [inline]
 call_netdevice_notifiers net/core/dev.c:1974 [inline]
 __dev_notify_flags+0xcf/0x200 net/core/dev.c:8183
 dev_change_flags+0xaa/0xd0 net/core/dev.c:8219
 do_setlink+0x626/0x1f40 net/core/rtnetlink.c:2598
 __rtnl_newlink+0x8e8/0xfb0 net/core/rtnetlink.c:3266
 rtnl_newlink+0x5f/0x90 net/core/rtnetlink.c:3391
 rtnetlink_rcv_msg+0x1d0/0x4e0 net/core/rtnetlink.c:5454
 netlink_rcv_skb+0xaf/0x260 net/netlink/af_netlink.c:2469
 rtnetlink_rcv+0x22/0x30 net/core/rtnetlink.c:5472
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x390/0x4c0 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x4cf/0x8a0 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0x98/0xc0 net/socket.c:672
 __sys_sendto+0x1e2/0x2c0 net/socket.c:2000
 __do_sys_sendto net/socket.c:2012 [inline]
 __se_sys_sendto net/socket.c:2008 [inline]
 __x64_sys_sendto+0x7e/0xa0 net/socket.c:2008
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9411 Comm: syz-executor.4 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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