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BUG: KCSAN: data-race in pcpu_alloc_noprof / pcpu_free_area

read-write to 0xffffffff88bdd3ac of 4 bytes by task 50 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+0x4dc/0x570 mm/percpu.c:1302
 free_percpu+0x1c6/0xb30 mm/percpu.c:2246
 xt_percpu_counter_free+0x63/0x80 net/netfilter/x_tables.c:1951
 cleanup_entry net/ipv4/netfilter/arp_tables.c:513 [inline]
 __arpt_unregister_table+0x107/0x1c0 net/ipv4/netfilter/arp_tables.c:1502
 arpt_unregister_table+0x3a/0x50 net/ipv4/netfilter/arp_tables.c:1586
 arptable_filter_net_exit+0x1c/0x30 net/ipv4/netfilter/arptable_filter.c:51
 ops_exit_list net/core/net_namespace.c:173 [inline]
 cleanup_net+0x475/0x810 net/core/net_namespace.c:626
 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 0xffffffff88bdd3ac of 4 bytes by task 3933 on cpu 0:
 pcpu_alloc_noprof+0x9a7/0x10c0 mm/percpu.c:1894
 alloc_vfsmnt+0xfe/0x300 fs/namespace.c:326
 clone_mnt+0x45/0x7a0 fs/namespace.c:1292
 copy_tree+0xba/0x7f0 fs/namespace.c:2125
 __do_loopback+0x111/0x210 fs/namespace.c:2742
 do_loopback+0x1dd/0x2d0 fs/namespace.c:2782
 path_mount+0x3d0/0xb30 fs/namespace.c:3828
 do_mount fs/namespace.c:3847 [inline]
 __do_sys_mount fs/namespace.c:4055 [inline]
 __se_sys_mount+0x27c/0x2d0 fs/namespace.c:4032
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4032
 x64_sys_call+0x203e/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000b -> 0x0000000c

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3933 Comm: syz-executor Not tainted 6.12.0-rc1-syzkaller-00165-g360c1f1f24c6 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
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