======================================
| [ 55.863054][ T67] #3: ffffffffaa807e88 (rtnl_mutex){+.+.}-{4:4}, at: cleanup_net (net/core/net_namespace.c:639)
| [ 55.863431][ T67] #4: ffffffffaa7f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   55.863857][   T67]
| [   55.863857][   T67] stack backtrace:
[   55.864488][   T67] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   55.864755][   T67] Workqueue: netns cleanup_net
[   55.865003][   T67] Call Trace:
[   55.865166][   T67]  <TASK>
[ 55.865271][ T67] dump_stack_lvl (lib/dump_stack.c:123)
[ 55.865473][ T67] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 55.865679][ T67] validate_chain (kernel/locking/lockdep.c:3894)
[ 55.865873][ T67] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 55.866069][ 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)
[ 55.866272][ T67] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 55.866434][ T67] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 55.866635][ T67] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 55.866839][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 55.867093][ T67] ? __lock_acquire (kernel/locking/lockdep.c:5226)
[ 55.867288][ T67] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 55.867477][ T67] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 55.867664][ T67] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 55.867865][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 55.868125][ 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)
[ 55.868279][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 55.868541][ T67] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 55.868749][ T67] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 55.868955][ T67] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 55.869160][ T67] __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))
[ 55.869369][ T67] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 55.869574][ T67] ? __pfx___netdev_upper_dev_unlink (net/core/dev.c:8151)
[ 55.869824][ T67] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 55.870214][ T67] ? __try_to_del_timer_sync (kernel/time/timer.c:1498)
[ 55.870424][ T67] ? __pfx___try_to_del_timer_sync (kernel/time/timer.c:1498)
[ 55.870682][ T67] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 55.871032][ T67] netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 55.871237][ T67] ? __pfx_netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 55.871490][ 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)
[ 55.871688][ T67] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 55.872029][ T67] ? netdev_master_upper_dev_get (net/core/dev.c:7230)
[ 55.872278][ T67] vrf_device_event (drivers/net/vrf.c:1110 drivers/net/vrf.c:1119 drivers/net/vrf.c:1804)
[ 55.872486][ T67] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 55.872692][ T67] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 55.873024][ T67] unregister_netdevice_many_notify (net/core/dev.c:11571)
[ 55.873273][ T67] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 55.873474][ T67] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11512)
[ 55.873849][ 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)
[ 55.874062][ T67] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 55.874266][ 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)
[ 55.874473][ T67] ? 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)
[ 55.874857][ T67] cleanup_net (net/core/net_namespace.c:644)
[ 55.875065][ T67] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 55.875278][ T67] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 55.875487][ T67] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 55.875839][ T67] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 55.876047][ T67] ? process_one_work (kernel/workqueue.c:3205)
[ 55.876258][ T67] process_one_work (kernel/workqueue.c:3229)
[ 55.876471][ T67] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 55.876817][ T67] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 55.877022][ T67] ? assign_work (kernel/workqueue.c:1200)
[ 55.877220][ T67] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 55.877428][ T67] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 55.877815][ T67] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 55.878022][ T67] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 55.878229][ T67] kthread (kernel/kthread.c:389)
[ 55.878404][ T67] ? __pfx_kthread (kernel/kthread.c:342)
[ 55.878749][ T67] ret_from_fork (arch/x86/kernel/process.c:147)
[ 55.878955][ T67] ? __pfx_kthread (kernel/kthread.c:342)


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