======================================
| [ 42.457942][ T68] #3: ffffffffb57e7a48 (rtnl_mutex){+.+.}-{4:4}, at: cleanup_net (net/core/net_namespace.c:639)
| [ 42.458317][ T68] #4: ffffffffb57d6630 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   42.458734][   T68]
| [   42.458734][   T68] stack backtrace:
[   42.459394][   T68] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   42.459675][   T68] Workqueue: netns cleanup_net
[   42.459904][   T68] Call Trace:
[   42.460082][   T68]  <TASK>
[ 42.460201][ T68] dump_stack_lvl (lib/dump_stack.c:123)
[ 42.460432][ T68] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 42.460662][ T68] validate_chain (kernel/locking/lockdep.c:3894)
[ 42.460893][ T68] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 42.461126][ T68] ? 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)
[ 42.461357][ T68] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 42.461535][ T68] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 42.461759][ T68] ? spin_bug (kernel/locking/spinlock_debug.c:57 kernel/locking/spinlock_debug.c:78)
[ 42.461930][ T68] ? debug_object_assert_init (./include/linux/err.h:81 lib/debugobjects.c:1010)
[ 42.462152][ T68] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 42.462392][ T68] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 42.462671][ T68] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 42.462893][ T68] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 42.463116][ T68] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 42.463335][ T68] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 42.463597][ T68] down_read (./arch/x86/include/asm/preempt.h:79 kernel/locking/rwsem.c:1246 kernel/locking/rwsem.c:1261 kernel/locking/rwsem.c:1526)
[ 42.463721][ T68] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 42.463896][ T68] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 42.464038][ T68] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 42.464179][ T68] __dev_close_many (net/core/dev.c:1537 (discriminator 3))
[ 42.464321][ T68] ? __pfx___dev_close_many (net/core/dev.c:1525)
[ 42.464483][ T68] dev_close_many (net/core/dev.c:1588)
[ 42.464633][ T68] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 42.464776][ T68] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 42.464959][ T68] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 42.465100][ T68] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 42.465269][ T68] vlan_device_event (net/8021q/vlan.c:451) 8021q
[ 42.465467][ T68] ? net_generic (./include/net/netns/generic.h:51) vxlan
[ 42.465625][ T68] ? __pfx_vlan_device_event (net/8021q/vlan.c:362) 8021q
[ 42.465810][ T68] ? __pfx_vxlan_netdevice_event (drivers/net/vxlan/vxlan_core.c:4737) vxlan
[ 42.466003][ T68] ? packet_notifier (net/packet/af_packet.c:4282)
[ 42.466150][ T68] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 42.466299][ T68] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 42.466450][ T68] dev_close_many (net/core/dev.c:1591)
[ 42.466591][ T68] ? __lock_release (kernel/locking/lockdep.c:5525)
[ 42.466734][ T68] ? __virt_addr_valid (./include/linux/rcupdate.h:347 ./include/linux/rcupdate.h:962 ./include/linux/mmzone.h:2058 arch/x86/mm/physaddr.c:65)
[ 42.466960][ T68] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 42.467190][ T68] unregister_netdevice_many_notify (net/core/dev.c:11549)
[ 42.467408][ T68] ? mark_held_locks (kernel/locking/lockdep.c:4321)
[ 42.467548][ T68] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11516)
[ 42.467752][ T68] ? 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)
[ 42.468067][ T68] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 42.468282][ T68] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 42.468817][ T68] ? 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)
[ 42.469035][ T68] ? 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)
[ 42.469811][ T68] cleanup_net (net/core/net_namespace.c:644)
[ 42.470039][ T68] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 42.470259][ T68] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 42.470761][ T68] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 42.470994][ T68] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 42.471219][ T68] ? process_one_work (kernel/workqueue.c:3205)
[ 42.471441][ T68] process_one_work (kernel/workqueue.c:3229)
[ 42.471667][ T68] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 42.471891][ T68] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 42.472257][ T68] ? assign_work (kernel/workqueue.c:1200)
[ 42.472489][ T68] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 42.472711][ T68] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 42.472998][ T68] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 42.473223][ T68] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 42.473442][ T68] kthread (kernel/kthread.c:389)
[ 42.473614][ T68] ? __pfx_kthread (kernel/kthread.c:342)
[ 42.473983][ T68] ret_from_fork (arch/x86/kernel/process.c:147)
[ 42.474202][ T68] ? __pfx_kthread (kernel/kthread.c:342)


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