======================================
| [ 15.420644][ T67] #3: ffffffffa0e07e88 (rtnl_mutex){+.+.}-{4:4}, at: cleanup_net (net/core/net_namespace.c:639)
| [ 15.420886][ T67] #4: ffffffffa0df6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   15.421160][   T67]
| [   15.421160][   T67] stack backtrace:
[   15.421571][   T67] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   15.421740][   T67] Workqueue: netns cleanup_net
[   15.421881][   T67] Call Trace:
[   15.421988][   T67]  <TASK>
[ 15.422061][ T67] dump_stack_lvl (lib/dump_stack.c:123)
[ 15.422202][ T67] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 15.422341][ T67] validate_chain (kernel/locking/lockdep.c:3894)
[ 15.422480][ T67] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 15.422625][ 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)
[ 15.422765][ T67] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 15.422871][ T67] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 15.423008][ T67] ? spin_bug (./include/linux/pid.h:232 kernel/locking/spinlock_debug.c:64 kernel/locking/spinlock_debug.c:78)
[ 15.423115][ T67] ? debug_object_assert_init (./include/linux/err.h:81 lib/debugobjects.c:1010)
[ 15.423255][ T67] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 15.423395][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 15.423566][ T67] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 15.423709][ T67] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 15.423847][ T67] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 15.423983][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 15.424174][ 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)
[ 15.424283][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 15.424457][ T67] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 15.424599][ T67] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 15.424744][ T67] __dev_close_many (net/core/dev.c:1537 (discriminator 3))
[ 15.424886][ T67] ? __pfx___dev_close_many (net/core/dev.c:1525)
[ 15.425029][ T67] dev_close_many (net/core/dev.c:1588)
[ 15.425179][ T67] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 15.425315][ T67] ? ipv6_mc_down (net/ipv6/mcast.c:1140 net/ipv6/mcast.c:2777)
[ 15.425457][ T67] vlan_device_event (net/8021q/vlan.c:451)
[ 15.425597][ T67] ? __pfx_vlan_device_event (net/8021q/vlan.c:362)
[ 15.425745][ T67] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 15.425883][ T67] ? packet_notifier (net/packet/af_packet.c:4282)
[ 15.426021][ T67] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 15.426159][ T67] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 15.426293][ T67] dev_close_many (net/core/dev.c:1591)
[ 15.426430][ T67] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 15.426568][ T67] unregister_netdevice_many_notify (net/core/dev.c:11549)
[ 15.426764][ T67] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 15.426909][ T67] ? net_generic (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:880 ./include/net/netns/generic.h:48)
[ 15.427051][ T67] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11516)
[ 15.427224][ T67] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 15.427364][ T67] ? unregister_netdevice_queue (net/core/dev.c:11501)
[ 15.427535][ T67] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 15.427715][ T67] ? net_generic (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:880 ./include/net/netns/generic.h:48)
[ 15.427866][ 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)
[ 15.428006][ 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)
[ 15.428178][ T67] cleanup_net (net/core/net_namespace.c:644)
[ 15.428317][ T67] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 15.428454][ T67] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 15.428587][ T67] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 15.428722][ T67] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 15.428865][ T67] ? process_one_work (kernel/workqueue.c:3205)
[ 15.429002][ T67] process_one_work (kernel/workqueue.c:3229)
[ 15.429143][ T67] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 15.429281][ T67] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 15.429421][ T67] ? assign_work (kernel/workqueue.c:1200)
[ 15.429563][ T67] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 15.429699][ T67] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 15.429875][ T67] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 15.430012][ T67] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 15.430147][ T67] kthread (kernel/kthread.c:389)
[ 15.430254][ T67] ? __pfx_kthread (kernel/kthread.c:342)
[ 15.430391][ T67] ret_from_fork (arch/x86/kernel/process.c:147)
[ 15.430530][ T67] ? __pfx_kthread (kernel/kthread.c:342)


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