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BUG: KCSAN: data-race in pcpu_alloc / pcpu_balance_workfn

write to 0xffffffff892dab5c of 4 bytes by task 9171 on cpu 0:
 pcpu_update_empty_pages mm/percpu.c:549 [inline]
 pcpu_chunk_populated mm/percpu.c:1455 [inline]
 pcpu_balance_workfn+0xc2b/0xeb0 mm/percpu.c:1898
 process_one_work+0x3cb/0x990 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x210/0x220 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffffffff892dab5c of 4 bytes by task 8823 on cpu 1:
 pcpu_alloc+0xb0f/0x10e0 mm/percpu.c:1706
 __alloc_percpu_gfp+0x22/0x30 mm/percpu.c:1760
 fib_nh_common_init net/ipv4/fib_semantics.c:580 [inline]
 fib_nh_init+0x75/0x2e0 net/ipv4/fib_semantics.c:619
 fib_create_info+0x1523/0x2fb0 net/ipv4/fib_semantics.c:1457
 fib_table_insert+0x130/0x1110 net/ipv4/fib_trie.c:1189
 fib_magic+0x195/0x1e0 net/ipv4/fib_frontend.c:1084
 fib_add_ifaddr+0xd5/0x310 net/ipv4/fib_frontend.c:1106
 fib_inetaddr_event+0xb5/0x210 net/ipv4/fib_frontend.c:1419
 notifier_call_chain kernel/notifier.c:83 [inline]
 __blocking_notifier_call_chain kernel/notifier.c:284 [inline]
 blocking_notifier_call_chain+0x73/0xe0 kernel/notifier.c:295
 __inet_insert_ifa+0x4ed/0x5d0 net/ipv4/devinet.c:553
 inet_rtm_newaddr+0x5a6/0xb00 net/ipv4/devinet.c:957
 rtnetlink_rcv_msg+0x71b/0x7b0 net/core/rtnetlink.c:5460
 netlink_rcv_skb+0x13e/0x240 net/netlink/af_netlink.c:2469
 rtnetlink_rcv+0x18/0x20 net/core/rtnetlink.c:5478
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x5e2/0x6b0 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x6d8/0x7a0 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 __sys_sendto+0x2ad/0x380 net/socket.c:1995
 __do_sys_sendto net/socket.c:2007 [inline]
 __se_sys_sendto net/socket.c:2003 [inline]
 __x64_sys_sendto+0x74/0x90 net/socket.c:2003
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8823 Comm: syz-executor.2 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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