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BUG: KCSAN: data-race in device_del / mm_update_next_owner

write to 0xffff8881026fb02c of 4 bytes by task 3051 on cpu 1:
 memalloc_noio_save include/linux/sched/mm.h:213 [inline]
 device_del+0x123/0x8f0 drivers/base/core.c:3260
 netdev_unregister_kobject+0xec/0x100 net/core/net-sysfs.c:1905
 rollback_registered_many+0xbe0/0xe50 net/core/dev.c:9522
 unregister_netdevice_many+0x2c/0x1a0 net/core/dev.c:10735
 ip6gre_exit_batch_net+0x496/0x4c0 net/ipv6/ip6_gre.c:1630
 ops_exit_list net/core/net_namespace.c:190 [inline]
 cleanup_net+0x4dc/0x900 net/core/net_namespace.c:604
 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:296

read to 0xffff8881026fb02c of 4 bytes by task 4623 on cpu 0:
 mm_update_next_owner+0x1d9/0x4e0 kernel/exit.c:388
 exit_mm+0x337/0x430 kernel/exit.c:500
 do_exit+0x41f/0x1690 kernel/exit.c:812
 do_group_exit+0xce/0x180 kernel/exit.c:922
 get_signal+0xdce/0x14e0 kernel/signal.c:2773
 arch_do_signal_or_restart+0x2a/0x270 arch/x86/kernel/signal.c:811
 handle_signal_work kernel/entry/common.c:147 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x11a/0x1b0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4623 Comm: syz-executor.2 Not tainted 5.11.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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