======================================
| [ 30.934759][ T11] #3: ffffffff8ec07e88 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12109)
| [ 30.935048][ T11] #4: ffffffff8ebf6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   30.935328][   T11]
| [   30.935328][   T11] stack backtrace:
[   30.935740][   T11] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   30.935912][   T11] Workqueue: netns cleanup_net
[   30.936057][   T11] Call Trace:
[   30.936164][   T11]  <TASK>
[ 30.936237][ T11] dump_stack_lvl (lib/dump_stack.c:123)
[ 30.936378][ T11] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 30.936517][ T11] validate_chain (kernel/locking/lockdep.c:3894)
[ 30.936659][ T11] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 30.936800][ T11] ? 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)
[ 30.936940][ T11] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 30.937046][ T11] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 30.937187][ T11] ? spin_bug (./include/linux/pid.h:232 kernel/locking/spinlock_debug.c:64 kernel/locking/spinlock_debug.c:78)
[ 30.937293][ T11] ? debug_object_assert_init (./include/linux/err.h:81 lib/debugobjects.c:1010)
[ 30.937434][ T11] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 30.937572][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 30.937745][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 30.937882][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 30.938021][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 30.938156][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 30.938329][ T11] down_read (./arch/x86/include/asm/preempt.h:79 kernel/locking/rwsem.c:1246 kernel/locking/rwsem.c:1261 kernel/locking/rwsem.c:1526)
[ 30.938435][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 30.938606][ T11] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 30.938748][ T11] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 30.938890][ T11] __dev_close_many (net/core/dev.c:1537 (discriminator 3))
[ 30.939032][ T11] ? __pfx___dev_close_many (net/core/dev.c:1525)
[ 30.939171][ T11] dev_close_many (net/core/dev.c:1588)
[ 30.939310][ T11] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 30.939451][ T11] ? ipv6_mc_down (net/ipv6/mcast.c:1140 net/ipv6/mcast.c:2777)
[ 30.939593][ T11] vlan_device_event (net/8021q/vlan.c:451)
[ 30.939735][ T11] ? __pfx_vlan_device_event (net/8021q/vlan.c:362)
[ 30.939877][ T11] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 30.940021][ T11] ? packet_notifier (net/packet/af_packet.c:4282)
[ 30.940160][ T11] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 30.940299][ T11] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 30.940437][ T11] dev_close_many (net/core/dev.c:1591)
[ 30.940578][ T11] ? fou_exit_net (net/ipv4/fou_core.c:1234)
[ 30.940718][ T11] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 30.940855][ T11] ? __pfx___mutex_trylock_common (kernel/locking/mutex.c:79)
[ 30.941033][ T11] unregister_netdevice_many_notify (net/core/dev.c:11549)
[ 30.941206][ T11] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11516)
[ 30.941375][ T11] ? default_device_exit_batch (net/core/dev.c:12109)
[ 30.941514][ T11] ? 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)
[ 30.941653][ T11] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 30.941794][ T11] ? unregister_netdevice_queue (net/core/dev.c:11501)
[ 30.941963][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 30.942132][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 30.942312][ T11] default_device_exit_batch (net/core/dev.c:12123)
[ 30.942450][ T11] ? __pfx_default_device_exit_batch (net/core/dev.c:12098)
[ 30.942621][ T11] ? ops_exit_list (net/core/net_namespace.c:171 (discriminator 3))
[ 30.942762][ T11] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 30.942898][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 30.943041][ T11] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 30.943179][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 30.943321][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 30.943460][ T11] ? process_one_work (kernel/workqueue.c:3205)
[ 30.943602][ T11] process_one_work (kernel/workqueue.c:3229)
[ 30.943743][ T11] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 30.943885][ T11] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 30.944028][ T11] ? assign_work (kernel/workqueue.c:1200)
[ 30.944169][ T11] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 30.944312][ T11] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 30.944453][ T11] kthread (kernel/kthread.c:389)
[ 30.944558][ T11] ? __pfx_kthread (kernel/kthread.c:342)
[ 30.944697][ T11] ret_from_fork (arch/x86/kernel/process.c:147)
[ 30.944837][ T11] ? __pfx_kthread (kernel/kthread.c:342)


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