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BUG: KCSAN: data-race in pcpu_alloc / pcpu_free_area

write to 0xffffffff8455f74c of 4 bytes by task 1767 on cpu 1:
 pcpu_update_empty_pages mm/percpu.c:559 [inline]
 pcpu_block_update_hint_free mm/percpu.c:994 [inline]
 pcpu_free_area+0x50c/0x5a0 mm/percpu.c:1254
 free_percpu+0x1d2/0x690 mm/percpu.c:2102
 xt_percpu_counter_free+0x5f/0x70 net/netfilter/x_tables.c:1889
 cleanup_entry+0x15a/0x180 net/ipv4/netfilter/ip_tables.c:655
 __do_replace+0x45e/0x580 net/ipv4/netfilter/ip_tables.c:1084
 do_replace net/ipv4/netfilter/ip_tables.c:1139 [inline]
 do_ipt_set_ctl+0x6ac/0x1630 net/ipv4/netfilter/ip_tables.c:1629
 nf_setsockopt+0x1a6/0x1c0 net/netfilter/nf_sockopt.c:101
 ip_setsockopt+0x2621/0x2a80 net/ipv4/ip_sockglue.c:1435
 tcp_setsockopt+0x8c/0xa0 net/ipv4/tcp.c:3656
 sock_common_setsockopt+0x5d/0x70 net/core/sock.c:3257
 __sys_setsockopt+0x18f/0x200 net/socket.c:2117
 __do_sys_setsockopt net/socket.c:2128 [inline]
 __se_sys_setsockopt net/socket.c:2125 [inline]
 __x64_sys_setsockopt+0x62/0x70 net/socket.c:2125
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff8455f74c of 4 bytes by task 1764 on cpu 0:
 pcpu_alloc+0xa33/0x1200 mm/percpu.c:1835
 __alloc_percpu+0x20/0x30 mm/percpu.c:1907
 xt_percpu_counter_alloc+0x6b/0x110 net/netfilter/x_tables.c:1869
 find_check_entry net/ipv4/netfilter/ip_tables.c:527 [inline]
 translate_table+0x97f/0xfc0 net/ipv4/netfilter/ip_tables.c:717
 do_replace net/ipv4/netfilter/ip_tables.c:1135 [inline]
 do_ipt_set_ctl+0x65f/0x1630 net/ipv4/netfilter/ip_tables.c:1629
 nf_setsockopt+0x1a6/0x1c0 net/netfilter/nf_sockopt.c:101
 ip_setsockopt+0x2621/0x2a80 net/ipv4/ip_sockglue.c:1435
 tcp_setsockopt+0x8c/0xa0 net/ipv4/tcp.c:3656
 sock_common_setsockopt+0x5d/0x70 net/core/sock.c:3257
 __sys_setsockopt+0x18f/0x200 net/socket.c:2117
 __do_sys_setsockopt net/socket.c:2128 [inline]
 __se_sys_setsockopt net/socket.c:2125 [inline]
 __x64_sys_setsockopt+0x62/0x70 net/socket.c:2125
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1764 Comm: syz-executor.2 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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