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BUG: KCSAN: data-race in pcpu_alloc_noprof / pcpu_balance_workfn

read-write to 0xffffffff8841f6ac of 4 bytes by task 8 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:2062 [inline]
 pcpu_balance_workfn+0x94e/0xa60 mm/percpu.c:2212
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
 worker_thread+0x526/0x730 kernel/workqueue.c:3393
 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 0xffffffff8841f6ac of 4 bytes by task 4363 on cpu 1:
 pcpu_alloc_noprof+0x9a7/0x10c0 mm/percpu.c:1894
 mm_alloc_cid_noprof include/linux/mm_types.h:1172 [inline]
 mm_init+0x47f/0x6f0 kernel/fork.c:1301
 dup_mm kernel/fork.c:1685 [inline]
 copy_mm+0x11e/0x11d0 kernel/fork.c:1737
 copy_process+0xee1/0x1f90 kernel/fork.c:2390
 kernel_clone+0x16a/0x570 kernel/fork.c:2797
 __do_sys_clone kernel/fork.c:2940 [inline]
 __se_sys_clone kernel/fork.c:2924 [inline]
 __x64_sys_clone+0xe8/0x120 kernel/fork.c:2924
 x64_sys_call+0x23e7/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:57
 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: 0x00000001 -> 0x00000004

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4363 Comm: syz-executor.3 Not tainted 6.10.0-rc3-syzkaller-00164-g44ef20baed8e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
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