syzbot

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BUG: KCSAN: data-race in device_del / kthread_is_per_cpu

write to 0xffff88812dfda02c of 4 bytes by task 1794 on cpu 1:
 memalloc_noio_save include/linux/sched/mm.h:218 [inline]
 device_del+0x123/0x8f0 drivers/base/core.c:3480
 netdev_unregister_kobject+0xec/0x100 net/core/net-sysfs.c:1921
 unregister_netdevice_many+0xbb4/0xf90 net/core/dev.c:11033
 default_device_exit_batch+0x237/0x260 net/core/dev.c:11536
 ops_exit_list net/core/net_namespace.c:178 [inline]
 cleanup_net+0x4dc/0x900 net/core/net_namespace.c:595
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2275
 worker_thread+0x636/0xae0 kernel/workqueue.c:2421
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88812dfda02c of 4 bytes by task 1031 on cpu 0:
 __to_kthread kernel/kthread.c:101 [inline]
 kthread_is_per_cpu+0x2d/0x80 kernel/kthread.c:540
 can_migrate_task+0xf/0x180 kernel/sched/fair.c:7615
 detach_tasks+0xab/0x380 kernel/sched/fair.c:7779
 load_balance+0x768/0xcc0 kernel/sched/fair.c:9679
 newidle_balance+0x10b/0x310 kernel/sched/fair.c:10643
 pick_next_task_fair+0x37/0x270 kernel/sched/fair.c:7203
 pick_next_task kernel/sched/core.c:4960 [inline]
 __schedule+0x256/0x5b0 kernel/sched/core.c:5111
 schedule+0x67/0x90 kernel/sched/core.c:5226
 schedule_hrtimeout_range_clock+0x115/0x1d0 kernel/time/hrtimer.c:2148
 schedule_hrtimeout_range+0x25/0x30 kernel/time/hrtimer.c:2202
 ep_poll fs/eventpoll.c:1848 [inline]
 do_epoll_wait+0xe80/0xf00 fs/eventpoll.c:2226
 __do_sys_epoll_wait fs/eventpoll.c:2238 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2233 [inline]
 __x64_sys_epoll_wait+0xf6/0x120 fs/eventpoll.c:2233
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1031 Comm: systemd-udevd Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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