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BUG: KCSAN: data-race in pcpu_alloc / pcpu_block_update_hint_alloc

read-write to 0xffffffff88314a4c of 4 bytes by task 20772 on cpu 1:
 pcpu_update_empty_pages mm/percpu.c:558 [inline]
 pcpu_block_update_hint_alloc+0x601/0x6e0 mm/percpu.c:872
 pcpu_alloc_area+0x559/0x580 mm/percpu.c:1209
 pcpu_alloc+0x46e/0x1020 mm/percpu.c:1770
 __alloc_percpu_gfp+0x22/0x30 mm/percpu.c:1893
 bpf_map_alloc_percpu+0xab/0x120 kernel/bpf/syscall.c:435
 prealloc_init kernel/bpf/hashtab.c:296 [inline]
 htab_map_alloc+0x807/0xc70 kernel/bpf/hashtab.c:508
 find_and_alloc_map kernel/bpf/syscall.c:122 [inline]
 map_create kernel/bpf/syscall.c:828 [inline]
 __do_sys_bpf+0x3fea/0x99c0 kernel/bpf/syscall.c:4362
 __se_sys_bpf kernel/bpf/syscall.c:4338 [inline]
 __x64_sys_bpf+0x3d/0x50 kernel/bpf/syscall.c:4338
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff88314a4c of 4 bytes by task 20763 on cpu 0:
 pcpu_alloc+0xa9b/0x1020 mm/percpu.c:1834
 __alloc_percpu_gfp+0x22/0x30 mm/percpu.c:1893
 bpf_map_alloc_percpu+0xab/0x120 kernel/bpf/syscall.c:435
 prealloc_init kernel/bpf/hashtab.c:296 [inline]
 htab_map_alloc+0x807/0xc70 kernel/bpf/hashtab.c:508
 find_and_alloc_map kernel/bpf/syscall.c:122 [inline]
 map_create kernel/bpf/syscall.c:828 [inline]
 __do_sys_bpf+0x3fea/0x99c0 kernel/bpf/syscall.c:4362
 __se_sys_bpf kernel/bpf/syscall.c:4338 [inline]
 __x64_sys_bpf+0x3d/0x50 kernel/bpf/syscall.c:4338
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20763 Comm: syz-executor.0 Not tainted 5.11.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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