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BUG: KCSAN: data-race in pcpu_alloc / pcpu_balance_workfn

write to 0xffffffff88f41ccc of 4 bytes by task 9727 on cpu 1:
 pcpu_update_empty_pages mm/percpu.c:559 [inline]
 pcpu_chunk_populated mm/percpu.c:1493 [inline]
 __pcpu_balance_workfn mm/percpu.c:2033 [inline]
 pcpu_balance_workfn+0xc7c/0xe40 mm/percpu.c:2069
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffffffff88f41ccc of 4 bytes by task 14702 on cpu 0:
 pcpu_alloc+0xaed/0x1090 mm/percpu.c:1835
 __alloc_percpu_gfp+0x22/0x30 mm/percpu.c:1894
 qdisc_alloc+0x17b/0x350 net/sched/sch_generic.c:828
 qdisc_create_dflt+0x48/0x260 net/sched/sch_generic.c:880
 mq_init+0x1c6/0x390 net/sched/sch_mq.c:90
 qdisc_create_dflt+0xc9/0x260 net/sched/sch_generic.c:887
 attach_default_qdiscs net/sched/sch_generic.c:1050 [inline]
 dev_activate+0xd7/0x9c0 net/sched/sch_generic.c:1101
 __dev_open+0x2e1/0x3a0 net/core/dev.c:1560
 __dev_change_flags+0x167/0x3f0 net/core/dev.c:8657
 dev_change_flags+0x55/0xc0 net/core/dev.c:8728
 devinet_ioctl+0x52b/0xfe0 net/ipv4/devinet.c:1142
 inet_ioctl+0x1f9/0x290 net/ipv4/af_inet.c:971
 packet_ioctl+0x12a/0x180 net/packet/af_packet.c:4161
 sock_do_ioctl+0x4d/0x210 net/socket.c:1039
 sock_ioctl+0x321/0x510 net/socket.c:1179
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 14702 Comm: syz-executor.3 Not tainted 5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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device syzkaller1 entered promiscuous mode