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BUG: KCSAN: data-race in pcpu_alloc / pcpu_balance_workfn

write to 0xffffffff892d3b5c of 4 bytes by task 4737 on cpu 0:
 pcpu_update_empty_pages mm/percpu.c:549 [inline]
 pcpu_chunk_populated mm/percpu.c:1455 [inline]
 pcpu_balance_workfn+0xc2b/0xeb0 mm/percpu.c:1898
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffffffff892d3b5c of 4 bytes by task 8845 on cpu 1:
 pcpu_alloc+0xb0f/0x10e0 mm/percpu.c:1706
 __alloc_percpu+0x20/0x30 mm/percpu.c:1773
 xt_percpu_counter_alloc+0x6b/0x110 net/netfilter/x_tables.c:1838
 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:1136 [inline]
 do_ipt_set_ctl+0x1cf/0x2a0 net/ipv4/netfilter/ip_tables.c:1672
 nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
 nf_setsockopt+0x18f/0x1b0 net/netfilter/nf_sockopt.c:115
 ip_setsockopt+0xc9/0xe0 net/ipv4/ip_sockglue.c:1319
 tcp_setsockopt+0x79/0x90 net/ipv4/tcp.c:3334
 sock_common_setsockopt+0x53/0x60 net/core/sock.c:3262
 __sys_setsockopt+0x27a/0x390 net/socket.c:2127
 __do_sys_setsockopt net/socket.c:2143 [inline]
 __se_sys_setsockopt net/socket.c:2140 [inline]
 __x64_sys_setsockopt+0x62/0x70 net/socket.c:2140
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8845 Comm: syz-executor.2 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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