======================================
| [ 1196.288336][ T67] #3: ffffffff91607e88 (rtnl_mutex){+.+.}-{4:4}, at: cleanup_net (net/core/net_namespace.c:639)
| [ 1196.288596][ T67] #4: ffffffff915f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [ 1196.288888][   T67]
| [ 1196.288888][   T67] stack backtrace:
[ 1196.289321][   T67] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 1196.289502][   T67] Workqueue: netns cleanup_net
[ 1196.289658][   T67] Call Trace:
[ 1196.289772][   T67]  <TASK>
[ 1196.289850][ T67] dump_stack_lvl (lib/dump_stack.c:123)
[ 1196.290003][ T67] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 1196.290154][ T67] validate_chain (kernel/locking/lockdep.c:3894)
[ 1196.290299][ T67] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 1196.290445][ 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)
[ 1196.290581][ T67] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 1196.290697][ T67] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 1196.290844][ T67] ? spin_bug (./include/linux/pid.h:232 kernel/locking/spinlock_debug.c:64 kernel/locking/spinlock_debug.c:78)
[ 1196.290950][ T67] ? debug_object_assert_init (./include/linux/err.h:81 lib/debugobjects.c:1010)
[ 1196.291100][ T67] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 1196.291251][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 1196.291433][ T67] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 1196.291577][ T67] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 1196.291722][ T67] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 1196.291863][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 1196.292039][ 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)
[ 1196.292148][ T67] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 1196.292332][ T67] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 1196.292477][ T67] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 1196.292622][ T67] __dev_close_many (net/core/dev.c:1537 (discriminator 3))
[ 1196.292775][ T67] ? __pfx___dev_close_many (net/core/dev.c:1525)
[ 1196.292919][ T67] dev_close_many (net/core/dev.c:1588)
[ 1196.293064][ T67] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 1196.293209][ T67] ? ipv6_mc_down (net/ipv6/mcast.c:1140 net/ipv6/mcast.c:2777)
[ 1196.293361][ T67] vlan_device_event (net/8021q/vlan.c:451)
[ 1196.293524][ T67] ? __pfx_vlan_device_event (net/8021q/vlan.c:362)
[ 1196.293671][ T67] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 1196.293818][ T67] ? packet_notifier (net/packet/af_packet.c:4282)
[ 1196.293957][ T67] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 1196.294095][ T67] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 1196.294241][ T67] dev_close_many (net/core/dev.c:1591)
[ 1196.294381][ T67] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 1196.294534][ T67] unregister_netdevice_many_notify (net/core/dev.c:11545)
[ 1196.294705][ T67] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 1196.294855][ T67] ? net_generic (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:880 ./include/net/netns/generic.h:48)
[ 1196.295009][ T67] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11512)
[ 1196.295186][ T67] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 1196.295323][ T67] ? unregister_netdevice_queue (net/core/dev.c:11497)
[ 1196.295497][ T67] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 1196.295692][ T67] ? net_generic (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:880 ./include/net/netns/generic.h:48)
[ 1196.295841][ 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)
[ 1196.295978][ 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)
[ 1196.296156][ T67] cleanup_net (net/core/net_namespace.c:644)
[ 1196.296305][ T67] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 1196.296452][ T67] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 1196.296599][ T67] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 1196.296741][ T67] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 1196.296884][ T67] ? process_one_work (kernel/workqueue.c:3205)
[ 1196.297034][ T67] process_one_work (kernel/workqueue.c:3229)
[ 1196.297180][ T67] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 1196.297321][ T67] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 1196.297464][ T67] ? assign_work (kernel/workqueue.c:1200)
[ 1196.297606][ T67] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 1196.297747][ T67] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 1196.297900][ T67] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 1196.298039][ T67] kthread (kernel/kthread.c:389)
[ 1196.298146][ T67] ? __pfx_kthread (kernel/kthread.c:342)
[ 1196.298284][ T67] ret_from_fork (arch/x86/kernel/process.c:147)
[ 1196.298426][ T67] ? __pfx_kthread (kernel/kthread.c:342)


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