======================================
| [ 29.943774][ T67] #3: ffffffffbc807e88 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12103)
| [ 29.944069][ T67] #4: ffffffffbc7f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   29.944352][   T67]
| [   29.944352][   T67] stack backtrace:
[   29.944762][   T67] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   29.944933][   T67] Workqueue: netns cleanup_net
[   29.945074][   T67] Call Trace:
[   29.945178][   T67]  <TASK>
[ 29.945256][ T67] dump_stack_lvl (lib/dump_stack.c:123)
[ 29.945398][ T67] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 29.945539][ T67] validate_chain (kernel/locking/lockdep.c:3894)
[ 29.945679][ T67] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 29.945823][ T67] ? 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)
[ 29.945959][ T67] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 29.946066][ T67] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 29.946203][ T67] ? spin_bug (./include/linux/pid.h:232 kernel/locking/spinlock_debug.c:64 kernel/locking/spinlock_debug.c:78)
[ 29.946312][ T67] ? debug_object_assert_init (./include/linux/err.h:81 lib/debugobjects.c:1010)
[ 29.946453][ T67] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 29.946590][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 29.946763][ T67] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 29.946910][ T67] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 29.947049][ T67] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 29.947187][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 29.947363][ T67] down_read (./arch/x86/include/asm/preempt.h:79 kernel/locking/rwsem.c:1246 kernel/locking/rwsem.c:1261 kernel/locking/rwsem.c:1526)
[ 29.947470][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 29.947643][ T67] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 29.947784][ T67] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 29.947921][ T67] __dev_close_many (net/core/dev.c:1537 (discriminator 3))
[ 29.948061][ T67] ? __pfx___dev_close_many (net/core/dev.c:1525)
[ 29.948203][ T67] dev_close_many (net/core/dev.c:1588)
[ 29.948346][ T67] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 29.948483][ T67] ? ipv6_mc_down (net/ipv6/mcast.c:1140 net/ipv6/mcast.c:2777)
[ 29.948627][ T67] vlan_device_event (net/8021q/vlan.c:451)
[ 29.948770][ T67] ? __pfx_vlan_device_event (net/8021q/vlan.c:362)
[ 29.948908][ T67] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 29.949049][ T67] ? packet_notifier (net/packet/af_packet.c:4282)
[ 29.949193][ T67] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 29.949337][ T67] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 29.949475][ T67] dev_close_many (net/core/dev.c:1591)
[ 29.949612][ T67] ? fou_exit_net (net/ipv4/fou_core.c:1234)
[ 29.949755][ T67] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 29.949894][ T67] ? __pfx___mutex_trylock_common (kernel/locking/mutex.c:79)
[ 29.950067][ T67] unregister_netdevice_many_notify (net/core/dev.c:11545)
[ 29.950240][ T67] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11512)
[ 29.950416][ T67] ? default_device_exit_batch (net/core/dev.c:12103)
[ 29.950556][ T67] ? 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)
[ 29.950694][ T67] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 29.950833][ T67] ? unregister_netdevice_queue (net/core/dev.c:11497)
[ 29.951006][ T67] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 29.951178][ T67] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 29.951351][ T67] default_device_exit_batch (net/core/dev.c:12117)
[ 29.951493][ T67] ? __pfx_default_device_exit_batch (net/core/dev.c:12092)
[ 29.951664][ T67] ? ops_exit_list (net/core/net_namespace.c:171 (discriminator 3))
[ 29.951804][ T67] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 29.951943][ T67] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 29.952082][ T67] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 29.952218][ T67] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 29.952356][ T67] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 29.952497][ T67] ? process_one_work (kernel/workqueue.c:3205)
[ 29.952637][ T67] process_one_work (kernel/workqueue.c:3229)
[ 29.952776][ T67] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 29.952915][ T67] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 29.953055][ T67] ? assign_work (kernel/workqueue.c:1200)
[ 29.953196][ T67] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 29.953335][ T67] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 29.953513][ T67] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 29.953652][ T67] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 29.953788][ T67] kthread (kernel/kthread.c:389)
[ 29.953900][ T67] ? __pfx_kthread (kernel/kthread.c:342)
[ 29.954039][ T67] ret_from_fork (arch/x86/kernel/process.c:147)
[ 29.954181][ T67] ? __pfx_kthread (kernel/kthread.c:342)


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