======================================
| [ 951.698543][ T66] #3: ffffffff90407e88 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12103)
| [ 951.698848][ T66] #4: ffffffff903f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [  951.699144][   T66]
| [  951.699144][   T66] stack backtrace:
[  951.699577][   T66] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  951.699754][   T66] Workqueue: netns cleanup_net
[  951.699908][   T66] Call Trace:
[  951.700018][   T66]  <TASK>
[ 951.700095][ T66] dump_stack_lvl (lib/dump_stack.c:123)
[ 951.700242][ T66] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 951.700388][ T66] validate_chain (kernel/locking/lockdep.c:3894)
[ 951.700534][ T66] ? __lock_acquire (kernel/locking/lockdep.c:5226)
[ 951.700684][ T66] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 951.700831][ 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)
[ 951.700975][ T66] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 951.701091][ T66] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 951.701243][ T66] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 951.701389][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 951.701571][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 951.701720][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 951.701867][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 951.702015][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 951.702203][ 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)
[ 951.702314][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 951.702492][ T66] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 951.702636][ T66] ? __mutex_unlock_slowpath (./arch/x86/include/asm/atomic64_64.h:101 ./include/linux/atomic/atomic-arch-fallback.h:4329 ./include/linux/atomic/atomic-long.h:1506 ./include/linux/atomic/atomic-instrumented.h:4481 kernel/locking/mutex.c:913)
[ 951.702782][ T66] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 951.702929][ 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))
[ 951.703076][ T66] ? __pfx___netdev_upper_dev_unlink (net/core/dev.c:8151)
[ 951.703260][ T66] ? synchronize_rcu_expedited (kernel/rcu/tree_exp.h:995 (discriminator 1))
[ 951.703448][ T66] ? __pfx_autoremove_wake_function (kernel/sched/wait.c:383)
[ 951.703624][ T66] ? __pfx___mutex_unlock_slowpath (kernel/locking/mutex.c:890)
[ 951.703804][ T66] netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 951.703948][ T66] ? __pfx_netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 951.704124][ 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)
[ 951.704274][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 951.704417][ T66] ? netdev_master_upper_dev_get (net/core/dev.c:7230)
[ 951.704601][ T66] ovs_netdev_detach_dev (net/openvswitch/vport-netdev.c:158 (discriminator 11)) openvswitch
[ 951.704802][ T66] ? ovs_netdev_get_vport (net/openvswitch/vport-netdev.c:196 (discriminator 3)) openvswitch
[ 951.705004][ T66] dp_device_event (net/openvswitch/dp_notify.c:77) openvswitch
[ 951.705190][ T66] ? trace_notifier_run (./include/trace/events/notifier.h:59 (discriminator 37))
[ 951.705338][ T66] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 951.705484][ T66] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 951.705639][ T66] unregister_netdevice_many_notify (net/core/dev.c:11571)
[ 951.705820][ T66] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11512)
[ 951.705995][ T66] ? default_device_exit_batch (net/core/dev.c:12103)
[ 951.706139][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 951.706282][ T66] ? unregister_netdevice_queue (net/core/dev.c:11497)
[ 951.706459][ T66] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 951.706802][ T66] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 951.707004][ T66] default_device_exit_batch (net/core/dev.c:12117)
[ 951.707148][ T66] ? __pfx_default_device_exit_batch (net/core/dev.c:12092)
[ 951.707320][ T66] ? ops_exit_list (net/core/net_namespace.c:171 (discriminator 3))
[ 951.707465][ T66] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 951.707610][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 951.707836][ T66] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 951.707982][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 951.708135][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 951.708283][ T66] ? process_one_work (kernel/workqueue.c:3205)
[ 951.708427][ T66] process_one_work (kernel/workqueue.c:3229)
[ 951.708653][ T66] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 951.708796][ T66] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 951.708942][ T66] ? assign_work (kernel/workqueue.c:1200)
[ 951.709092][ T66] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 951.709236][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 951.709416][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 951.709560][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 951.709787][ T66] kthread (kernel/kthread.c:389)
[ 951.709898][ T66] ? __pfx_kthread (kernel/kthread.c:342)
[ 951.710039][ T66] ret_from_fork (arch/x86/kernel/process.c:147)
[ 951.710270][ T66] ? __pfx_kthread (kernel/kthread.c:342)


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