======================================
| [ 18.334258][ T66] #3: ffffffffbc407e88 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12103)
| [ 18.334558][ T66] #4: ffffffffbc3f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   18.334855][   T66]
| [   18.334855][   T66] stack backtrace:
[   18.335298][   T66] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   18.335481][   T66] Workqueue: netns cleanup_net
[   18.335634][   T66] Call Trace:
[   18.335746][   T66]  <TASK>
[ 18.335825][ T66] dump_stack_lvl (lib/dump_stack.c:123)
[ 18.335977][ T66] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 18.336128][ T66] validate_chain (kernel/locking/lockdep.c:3894)
[ 18.336282][ T66] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 18.336432][ T66] ? hlock_class (./arch/x86/include/asm/bitops.h:227 ./arch/x86/include/asm/bitops.h:239 ./include/asm-generic/bitops/instrumented-non-atomic.h:142 kernel/locking/lockdep.c:228)
[ 18.336577][ T66] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 18.336691][ T66] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 18.336844][ T66] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 18.336992][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 18.337180][ T66] ? __lock_acquire (kernel/locking/lockdep.c:5226)
[ 18.337328][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 18.337478][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 18.337627][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 18.337774][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 18.337959][ T66] down_read (./arch/x86/include/asm/preempt.h:79 kernel/locking/rwsem.c:1246 kernel/locking/rwsem.c:1261 kernel/locking/rwsem.c:1526)
[ 18.338076][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 18.338261][ T66] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 18.338410][ T66] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 18.338561][ T66] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 18.338710][ T66] __netdev_upper_dev_unlink (net/core/dev.c:8000 (discriminator 11) net/core/dev.c:8017 (discriminator 11) net/core/dev.c:8167 (discriminator 11))
[ 18.338860][ T66] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 18.339009][ T66] ? __pfx___netdev_upper_dev_unlink (net/core/dev.c:8151)
[ 18.339193][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 18.339377][ T66] ? __try_to_del_timer_sync (kernel/time/timer.c:1498)
[ 18.339527][ T66] ? __pfx___try_to_del_timer_sync (kernel/time/timer.c:1498)
[ 18.339714][ T66] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 18.339867][ T66] netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 18.340015][ T66] ? __pfx_netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 18.340200][ T66] ? mutex_is_locked (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-long.h:38 ./include/linux/atomic/atomic-instrumented.h:3189 kernel/locking/mutex.h:47 kernel/locking/mutex.c:66)
[ 18.340350][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 18.340500][ T66] ? netdev_master_upper_dev_get (net/core/dev.c:7230)
[ 18.340685][ T66] vrf_device_event (drivers/net/vrf.c:1110 drivers/net/vrf.c:1119 drivers/net/vrf.c:1804)
[ 18.340835][ T66] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 18.340985][ T66] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 18.341133][ T66] unregister_netdevice_many_notify (net/core/dev.c:11571)
[ 18.341320][ T66] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11512)
[ 18.341507][ T66] ? default_device_exit_batch (net/core/dev.c:12103)
[ 18.341660][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 18.341808][ T66] ? unregister_netdevice_queue (net/core/dev.c:11497)
[ 18.341993][ T66] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 18.342186][ T66] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 18.342381][ T66] default_device_exit_batch (net/core/dev.c:12117)
[ 18.342531][ T66] ? __pfx_default_device_exit_batch (net/core/dev.c:12092)
[ 18.342715][ T66] ? ops_exit_list (net/core/net_namespace.c:171 (discriminator 3))
[ 18.342869][ T66] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 18.343019][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 18.343168][ T66] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 18.343316][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 18.343467][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 18.343617][ T66] ? process_one_work (kernel/workqueue.c:3205)
[ 18.343767][ T66] process_one_work (kernel/workqueue.c:3229)
[ 18.343917][ T66] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 18.344067][ T66] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 18.344217][ T66] ? assign_work (kernel/workqueue.c:1200)
[ 18.344366][ T66] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 18.344515][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 18.344707][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 18.344857][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 18.345013][ T66] kthread (kernel/kthread.c:389)
[ 18.345130][ T66] ? __pfx_kthread (kernel/kthread.c:342)
[ 18.345280][ T66] ret_from_fork (arch/x86/kernel/process.c:147)
[ 18.345430][ T66] ? __pfx_kthread (kernel/kthread.c:342)


Finger prints:
print_deadlock_bug:validate_chain:__lock_acquire:down_read:blocking_notifier_call_chain