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BUG: KCSAN: data-race in pcpu_alloc / pcpu_balance_workfn

read-write to 0xffffffff8712631c of 4 bytes by task 3175 on cpu 0:
 pcpu_update_empty_pages mm/percpu.c:602 [inline]
 pcpu_chunk_populated mm/percpu.c:1531 [inline]
 pcpu_balance_populated mm/percpu.c:2088 [inline]
 pcpu_balance_workfn+0x94e/0xa50 mm/percpu.c:2238
 process_one_work kernel/workqueue.c:2633 [inline]
 process_scheduled_works+0x5b8/0xa40 kernel/workqueue.c:2706
 worker_thread+0x525/0x730 kernel/workqueue.c:2787
 kthread+0x1d7/0x210 kernel/kthread.c:388
 ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

read to 0xffffffff8712631c of 4 bytes by task 12742 on cpu 1:
 pcpu_alloc+0x9be/0x10c0 mm/percpu.c:1868
 __alloc_percpu_gfp+0x26/0x30 mm/percpu.c:1930
 bpf_map_alloc_percpu+0xaa/0x200 kernel/bpf/syscall.c:465
 prealloc_init+0x19f/0x470 kernel/bpf/hashtab.c:338
 htab_map_alloc+0x715/0x9e0 kernel/bpf/hashtab.c:569
 map_create+0x713/0xa40 kernel/bpf/syscall.c:1237
 __sys_bpf+0x62a/0x780 kernel/bpf/syscall.c:5439
 __do_sys_bpf kernel/bpf/syscall.c:5561 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5559 [inline]
 __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5559
 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+0x63/0x6b

value changed: 0x00000003 -> 0x00000004

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12742 Comm: syz-executor.1 Not tainted 6.8.0-rc4-syzkaller-00331-gc1ca10ceffbb #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
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