======================================
| [ 55.544113][ T66] #3: ffffffff8d7e7a48 (rtnl_mutex){+.+.}-{4:4}, at: cleanup_net (net/core/net_namespace.c:639)
| [ 55.544377][ T66] #4: ffffffff8d7d6630 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   55.544666][   T66]
| [   55.544666][   T66] stack backtrace:
[   55.545104][   T66] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   55.545285][   T66] Workqueue: netns cleanup_net
[   55.545465][   T66] Call Trace:
[   55.545577][   T66]  <TASK>
[ 55.545654][ T66] dump_stack_lvl (lib/dump_stack.c:123)
[ 55.545808][ T66] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 55.545955][ T66] validate_chain (kernel/locking/lockdep.c:3894)
[ 55.546103][ T66] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 55.546253][ 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)
[ 55.546397][ T66] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 55.546513][ T66] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 55.546657][ T66] ? spin_bug (kernel/locking/spinlock_debug.c:57 kernel/locking/spinlock_debug.c:78)
[ 55.546771][ T66] ? debug_object_assert_init (./include/linux/err.h:81 lib/debugobjects.c:1010)
[ 55.546920][ T66] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 55.547068][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 55.547250][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 55.547400][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 55.547547][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 55.547693][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 55.547955][ 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)
[ 55.548067][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 55.548248][ T66] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 55.548395][ T66] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 55.548622][ T66] __dev_close_many (net/core/dev.c:1537 (discriminator 3))
[ 55.548771][ T66] ? __pfx___dev_close_many (net/core/dev.c:1525)
[ 55.548921][ T66] dev_close_many (net/core/dev.c:1588)
[ 55.549144][ T66] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 55.549289][ T66] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 55.549430][ T66] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 55.549581][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 55.549802][ T66] vlan_device_event (net/8021q/vlan.c:451) 8021q
[ 55.549990][ T66] ? net_generic (./include/net/netns/generic.h:51) vxlan
[ 55.550148][ T66] ? __pfx_vlan_device_event (net/8021q/vlan.c:362) 8021q
[ 55.550329][ T66] ? __pfx_vxlan_netdevice_event (drivers/net/vxlan/vxlan_core.c:4737) vxlan
[ 55.550518][ T66] ? packet_notifier (net/packet/af_packet.c:4282)
[ 55.550669][ T66] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 55.550813][ T66] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 55.550958][ T66] dev_close_many (net/core/dev.c:1591)
[ 55.551109][ T66] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 55.551255][ T66] ? __virt_addr_valid (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:962 ./include/linux/mmzone.h:2058 arch/x86/mm/physaddr.c:65)
[ 55.551401][ T66] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 55.551622][ T66] unregister_netdevice_many_notify (net/core/dev.c:11545)
[ 55.551804][ T66] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 55.551953][ T66] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11512)
[ 55.552300][ 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)
[ 55.552457][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 55.552603][ T66] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 55.552793][ 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)
[ 55.552938][ T66] ? nexthop_net_exit_batch_rtnl (net/ipv4/nexthop.c:585 net/ipv4/nexthop.c:2158 net/ipv4/nexthop.c:2666 net/ipv4/nexthop.c:4010)
[ 55.553123][ T66] cleanup_net (net/core/net_namespace.c:644)
[ 55.553284][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 55.553436][ T66] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 55.553671][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 55.553894][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 55.554039][ T66] ? process_one_work (kernel/workqueue.c:3205)
[ 55.554189][ T66] process_one_work (kernel/workqueue.c:3229)
[ 55.554353][ T66] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 55.554500][ T66] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 55.554642][ T66] ? assign_work (kernel/workqueue.c:1200)
[ 55.554794][ T66] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 55.554942][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 55.555121][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 55.555269][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 55.555428][ T66] kthread (kernel/kthread.c:389)
[ 55.555539][ T66] ? __pfx_kthread (kernel/kthread.c:342)
[ 55.555683][ T66] ret_from_fork (arch/x86/kernel/process.c:147)
[ 55.555837][ T66] ? __pfx_kthread (kernel/kthread.c:342)


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