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BUG: KCSAN: data-race in pcpu_alloc / pcpu_chunk_populated

write to 0xffffffff88afae40 of 4 bytes by task 9926 on cpu 1:
 pcpu_update_empty_pages mm/percpu.c:548 [inline]
 pcpu_chunk_populated+0xe2/0x100 mm/percpu.c:1454
 pcpu_balance_workfn+0xa13/0xc80 mm/percpu.c:1892
 process_one_work+0x424/0x930 kernel/workqueue.c:2268
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
 kthread+0x203/0x230 kernel/kthread.c:268
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffffffff88afae40 of 4 bytes by task 9072 on cpu 0:
 pcpu_alloc+0x3c2/0xd00 mm/percpu.c:1700
 __alloc_percpu_gfp+0x2d/0x40 mm/percpu.c:1754
 fib_nh_common_init+0x5f/0x1f0 net/ipv4/fib_semantics.c:580
 fib_nh_init+0x74/0x200 net/ipv4/fib_semantics.c:619
 fib_create_info+0x15e1/0x2860 net/ipv4/fib_semantics.c:1457
 fib_table_insert+0xf2/0xd30 net/ipv4/fib_trie.c:1189
 fib_magic.isra.0+0x273/0x2c0 net/ipv4/fib_frontend.c:1084
 fib_add_ifaddr+0x326/0x330 net/ipv4/fib_frontend.c:1128
 fib_netdev_event+0x1a9/0x220 net/ipv4/fib_frontend.c:1465
 notifier_call_chain+0xda/0x160 kernel/notifier.c:83
 __raw_notifier_call_chain kernel/notifier.c:361 [inline]
 raw_notifier_call_chain+0x33/0x50 kernel/notifier.c:368
 call_netdevice_notifiers_info net/core/dev.c:1948 [inline]
 call_netdevice_notifiers_info+0x96/0x110 net/core/dev.c:1933
 call_netdevice_notifiers_extack net/core/dev.c:1960 [inline]
 call_netdevice_notifiers net/core/dev.c:1974 [inline]
 __dev_notify_flags+0xcf/0x200 net/core/dev.c:8183
 dev_change_flags+0xaa/0xd0 net/core/dev.c:8219
 do_setlink+0x626/0x1f40 net/core/rtnetlink.c:2598
 __rtnl_newlink+0x8e8/0xfb0 net/core/rtnetlink.c:3266
 rtnl_newlink+0x5f/0x90 net/core/rtnetlink.c:3391
 rtnetlink_rcv_msg+0x1d0/0x4e0 net/core/rtnetlink.c:5454
 netlink_rcv_skb+0xaf/0x260 net/netlink/af_netlink.c:2469
 rtnetlink_rcv+0x22/0x30 net/core/rtnetlink.c:5472
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x390/0x4c0 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x4cf/0x8a0 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0x98/0xc0 net/socket.c:672
 __sys_sendto+0x1e2/0x2c0 net/socket.c:2000
 __do_sys_sendto net/socket.c:2012 [inline]
 __se_sys_sendto net/socket.c:2008 [inline]
 __x64_sys_sendto+0x7e/0xa0 net/socket.c:2008
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9072 Comm: syz-executor.2 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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