======================================
| [ 56.029954][ T66] #3: ffffffffb6207e88 (rtnl_mutex){+.+.}-{4:4}, at: cleanup_net (net/core/net_namespace.c:639)
| [ 56.030226][ T66] #4: ffffffffb61f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   56.030533][   T66]
| [   56.030533][   T66] stack backtrace:
[   56.031004][   T66] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   56.031191][   T66] Workqueue: netns cleanup_net
[   56.031350][   T66] Call Trace:
[   56.031465][   T66]  <TASK>
[ 56.031545][ T66] dump_stack_lvl (lib/dump_stack.c:123)
[ 56.031705][ T66] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 56.031861][ T66] validate_chain (kernel/locking/lockdep.c:3894)
[ 56.032004][ T66] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 56.032159][ 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)
[ 56.032309][ T66] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 56.032424][ T66] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 56.032576][ T66] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 56.032726][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 56.032918][ T66] ? __lock_acquire (kernel/locking/lockdep.c:5226)
[ 56.033070][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 56.033216][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 56.033365][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 56.033512][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 56.033697][ 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)
[ 56.033814][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 56.033997][ T66] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 56.034150][ T66] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 56.034301][ T66] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 56.034449][ 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))
[ 56.034608][ T66] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 56.034758][ T66] ? __pfx___netdev_upper_dev_unlink (net/core/dev.c:8151)
[ 56.034945][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 56.035130][ T66] ? __try_to_del_timer_sync (kernel/time/timer.c:1498)
[ 56.035291][ T66] ? __pfx___try_to_del_timer_sync (kernel/time/timer.c:1498)
[ 56.035473][ T66] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 56.035619][ T66] netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 56.035767][ T66] ? __pfx_netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 56.035960][ 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)
[ 56.036106][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 56.036250][ T66] ? netdev_master_upper_dev_get (net/core/dev.c:7230)
[ 56.036452][ T66] vrf_device_event (drivers/net/vrf.c:1110 drivers/net/vrf.c:1119 drivers/net/vrf.c:1804)
[ 56.036604][ T66] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 56.036755][ T66] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 56.036904][ T66] unregister_netdevice_many_notify (net/core/dev.c:11575)
[ 56.037088][ T66] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 56.037250][ T66] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11516)
[ 56.037438][ 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)
[ 56.037595][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 56.037746][ 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)
[ 56.037902][ 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)
[ 56.038089][ T66] cleanup_net (net/core/net_namespace.c:644)
[ 56.038241][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 56.038393][ T66] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 56.038543][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 56.038777][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 56.038929][ T66] ? process_one_work (kernel/workqueue.c:3205)
[ 56.039087][ T66] process_one_work (kernel/workqueue.c:3229)
[ 56.039242][ T66] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 56.039395][ T66] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 56.039547][ T66] ? assign_work (kernel/workqueue.c:1200)
[ 56.039704][ T66] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 56.039865][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 56.040055][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 56.040208][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 56.040439][ T66] kthread (kernel/kthread.c:389)
[ 56.040558][ T66] ? __pfx_kthread (kernel/kthread.c:342)
[ 56.040706][ T66] ret_from_fork (arch/x86/kernel/process.c:147)
[ 56.040859][ T66] ? __pfx_kthread (kernel/kthread.c:342)


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