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BUG: KCSAN: data-race in pcpu_alloc / pcpu_block_update_hint_alloc

read-write to 0xffffffff884054dc of 4 bytes by task 17077 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+0x49f/0x4d0 mm/percpu.c:1258
 pcpu_alloc+0x4b3/0x10d0 mm/percpu.c:1808
 __alloc_percpu_gfp+0x26/0x30 mm/percpu.c:1930
 bpf_map_alloc_percpu+0xab/0x200 kernel/bpf/syscall.c:466
 prealloc_init+0x19f/0x470 kernel/bpf/hashtab.c:338
 htab_map_alloc+0x637/0x8f0 kernel/bpf/hashtab.c:573
 map_create+0x83c/0xb90 kernel/bpf/syscall.c:1320
 __sys_bpf+0x667/0x7a0 kernel/bpf/syscall.c:5642
 __do_sys_bpf kernel/bpf/syscall.c:5767 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5765 [inline]
 __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5765
 x64_sys_call+0x86c/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:322
 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+0x77/0x7f

read to 0xffffffff884054dc of 4 bytes by task 17086 on cpu 0:
 pcpu_alloc+0x9aa/0x10d0 mm/percpu.c:1868
 __alloc_percpu+0x24/0x30 mm/percpu.c:1943
 mpls_add_dev net/mpls/af_mpls.c:1465 [inline]
 mpls_dev_notify+0x182/0x8f0 net/mpls/af_mpls.c:1618
 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:1950
 call_netdevice_notifiers_extack net/core/dev.c:1988 [inline]
 call_netdevice_notifiers net/core/dev.c:2002 [inline]
 register_netdevice+0xc63/0xde0 net/core/dev.c:10316
 register_netdev+0x3b/0x50 net/core/dev.c:10413
 ip6gre_init_net+0x1d9/0x250 net/ipv6/ip6_gre.c:1625
 ops_init+0x201/0x2d0 net/core/net_namespace.c:136
 setup_net+0x2ea/0x7c0 net/core/net_namespace.c:340
 copy_net_ns+0x389/0x520 net/core/net_namespace.c:505
 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:3323
 __do_sys_unshare kernel/fork.c:3394 [inline]
 __se_sys_unshare kernel/fork.c:3392 [inline]
 __x64_sys_unshare+0x1f/0x30 kernel/fork.c:3392
 x64_sys_call+0x21e5/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:273
 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+0x77/0x7f

value changed: 0x00000004 -> 0xfffffffc

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 17086 Comm: syz-executor.3 Tainted: G        W          6.9.0-rc5-syzkaller-00036-g9d1ddab261f3 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
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