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BUG: KCSAN: data-race in pcpu_alloc_noprof / pcpu_block_update_hint_alloc

read-write to 0xffffffff88bdd3ac of 4 bytes by task 11096 on cpu 1:
 pcpu_update_empty_pages mm/percpu.c:602 [inline]
 pcpu_block_update_hint_alloc+0x5db/0x6a0 mm/percpu.c:923
 pcpu_alloc_area+0x488/0x4b0 mm/percpu.c:1258
 pcpu_alloc_noprof+0x4b3/0x10c0 mm/percpu.c:1834
 bpf_map_alloc_percpu+0xad/0x210 kernel/bpf/syscall.c:466
 bpf_array_alloc_percpu kernel/bpf/arraymap.c:38 [inline]
 array_map_alloc+0x2aa/0x390 kernel/bpf/arraymap.c:152
 map_create+0x850/0xb70 kernel/bpf/syscall.c:1341
 __sys_bpf+0x667/0x7a0 kernel/bpf/syscall.c:5616
 __do_sys_bpf kernel/bpf/syscall.c:5741 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5739 [inline]
 __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5739
 x64_sys_call+0x2625/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:322
 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

read to 0xffffffff88bdd3ac of 4 bytes by task 11100 on cpu 0:
 pcpu_alloc_noprof+0x9a7/0x10c0 mm/percpu.c:1894
 snmp6_alloc_dev net/ipv6/addrconf.c:344 [inline]
 ipv6_add_dev+0x2ee/0xab0 net/ipv6/addrconf.c:409
 addrconf_notify+0x407/0x950 net/ipv6/addrconf.c:3655
 notifier_call_chain kernel/notifier.c:93 [inline]
 raw_notifier_call_chain+0x6f/0x1d0 kernel/notifier.c:461
 call_netdevice_notifiers_info+0xae/0x100 net/core/dev.c:1996
 call_netdevice_notifiers_extack net/core/dev.c:2034 [inline]
 call_netdevice_notifiers net/core/dev.c:2048 [inline]
 register_netdevice+0xca9/0xe30 net/core/dev.c:10520
 register_netdev+0x3b/0x50 net/core/dev.c:10624
 loopback_net_init+0x59/0x100 drivers/net/loopback.c:217
 ops_init+0x1c9/0x260 net/core/net_namespace.c:139
 setup_net+0x14d/0x600 net/core/net_namespace.c:356
 copy_net_ns+0x290/0x430 net/core/net_namespace.c:494
 create_new_namespaces+0x228/0x430 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0xe6/0x120 kernel/nsproxy.c:228
 ksys_unshare+0x3da/0x720 kernel/fork.c:3315
 __do_sys_unshare kernel/fork.c:3386 [inline]
 __se_sys_unshare kernel/fork.c:3384 [inline]
 __x64_sys_unshare+0x1f/0x30 kernel/fork.c:3384
 x64_sys_call+0x2c8d/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:273
 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: 0x00000004 -> 0xfffffffd

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 11100 Comm: syz.2.3258 Tainted: G        W          6.12.0-rc1-syzkaller-00042-gf23aa4c0761a #0
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
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lo speed is unknown, defaulting to 1000