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BUG: KCSAN: data-race in device_del / mm_update_next_owner

write to 0xffff88803099502c of 4 bytes by task 24175 on cpu 0:
 memalloc_noio_restore include/linux/sched/mm.h:227 [inline]
 device_del+0x8a0/0x8f0 drivers/base/core.c:3284
 netdev_unregister_kobject+0xe1/0xf0 net/core/net-sysfs.c:1905
 rollback_registered_many+0xbd0/0xe40 net/core/dev.c:9522
 unregister_netdevice_many+0x2e/0x1a0 net/core/dev.c:10730
 vti6_exit_batch_net+0x183/0x1b0 net/ipv6/ip6_vti.c:1186
 ops_exit_list net/core/net_namespace.c:190 [inline]
 cleanup_net+0x4cc/0x8e0 net/core/net_namespace.c:604
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88803099502c of 4 bytes by task 28363 on cpu 1:
 mm_update_next_owner+0x1d9/0x4e0 kernel/exit.c:388
 exit_mm+0x327/0x420 kernel/exit.c:500
 do_exit+0x41f/0x1690 kernel/exit.c:812
 do_group_exit+0x16f/0x170 kernel/exit.c:922
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 28363 Comm: syz-executor.0 Not tainted 5.11.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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