======================================
| [ 14.638072][ T66] #3: ffffffffbaa07e88 (rtnl_mutex){+.+.}-{4:4}, at: cleanup_net (net/core/net_namespace.c:639)
| [ 14.638325][ T66] #4: ffffffffba9f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   14.638607][   T66]
| [   14.638607][   T66] stack backtrace:
[   14.639012][   T66] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   14.639181][   T66] Workqueue: netns cleanup_net
[   14.639322][   T66] Call Trace:
[   14.639429][   T66]  <TASK>
[ 14.639501][ T66] dump_stack_lvl (lib/dump_stack.c:123)
[ 14.639644][ T66] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 14.639785][ T66] validate_chain (kernel/locking/lockdep.c:3894)
[ 14.639924][ T66] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 14.640064][ 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)
[ 14.640209][ T66] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 14.640314][ T66] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 14.640451][ T66] ? spin_bug (./include/linux/pid.h:232 kernel/locking/spinlock_debug.c:64 kernel/locking/spinlock_debug.c:78)
[ 14.640555][ T66] ? debug_object_assert_init (./include/linux/err.h:81 lib/debugobjects.c:1010)
[ 14.640700][ T66] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 14.640837][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 14.641007][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 14.641145][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 14.641285][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 14.641421][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 14.641590][ 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)
[ 14.641698][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 14.641868][ T66] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 14.642006][ T66] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 14.642143][ T66] __dev_close_many (net/core/dev.c:1537 (discriminator 3))
[ 14.642279][ T66] ? __pfx___dev_close_many (net/core/dev.c:1525)
[ 14.642417][ T66] dev_close_many (net/core/dev.c:1588)
[ 14.642554][ T66] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 14.642692][ T66] ? ipv6_mc_down (net/ipv6/mcast.c:1140 net/ipv6/mcast.c:2777)
[ 14.642831][ T66] vlan_device_event (net/8021q/vlan.c:451)
[ 14.642969][ T66] ? __pfx_vlan_device_event (net/8021q/vlan.c:362)
[ 14.643103][ T66] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 14.643240][ T66] ? packet_notifier (net/packet/af_packet.c:4282)
[ 14.643376][ T66] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 14.643513][ T66] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 14.643651][ T66] dev_close_many (net/core/dev.c:1591)
[ 14.643789][ T66] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 14.643928][ T66] unregister_netdevice_many_notify (net/core/dev.c:11545)
[ 14.644096][ T66] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 14.644234][ T66] ? net_generic (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:880 ./include/net/netns/generic.h:48)
[ 14.644371][ T66] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11512)
[ 14.644543][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 14.644682][ T66] ? unregister_netdevice_queue (net/core/dev.c:11497)
[ 14.644850][ T66] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 14.645018][ T66] ? net_generic (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:880 ./include/net/netns/generic.h:48)
[ 14.645156][ 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)
[ 14.645293][ 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)
[ 14.645462][ T66] cleanup_net (net/core/net_namespace.c:644)
[ 14.645600][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 14.645738][ T66] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 14.645870][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 14.646007][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 14.646144][ T66] ? process_one_work (kernel/workqueue.c:3205)
[ 14.646292][ T66] process_one_work (kernel/workqueue.c:3229)
[ 14.646430][ T66] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 14.646568][ T66] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 14.646709][ T66] ? assign_work (kernel/workqueue.c:1200)
[ 14.646847][ T66] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 14.646982][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 14.647161][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 14.647297][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 14.647432][ T66] kthread (kernel/kthread.c:389)
[ 14.647538][ T66] ? __pfx_kthread (kernel/kthread.c:342)
[ 14.647672][ T66] ret_from_fork (arch/x86/kernel/process.c:147)
[ 14.647809][ T66] ? __pfx_kthread (kernel/kthread.c:342)


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