======================================
| [ 249.265381][ T11] #3: ffffffff8a807e88 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12103)
| [ 249.265668][ T11] #4: ffffffff8a7f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [  249.265954][   T11]
| [  249.265954][   T11] stack backtrace:
[  249.266389][   T11] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  249.266572][   T11] Workqueue: netns cleanup_net
[  249.266722][   T11] Call Trace:
[  249.266826][   T11]  <TASK>
[ 249.266907][ T11] dump_stack_lvl (lib/dump_stack.c:123)
[ 249.267056][ T11] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 249.267206][ T11] validate_chain (kernel/locking/lockdep.c:3894)
[ 249.267352][ T11] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 249.267503][ 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)
[ 249.267642][ T11] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 249.267751][ T11] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 249.267897][ T11] ? spin_bug (./include/linux/pid.h:232 kernel/locking/spinlock_debug.c:64 kernel/locking/spinlock_debug.c:78)
[ 249.268007][ T11] ? debug_object_assert_init (./include/linux/err.h:81 lib/debugobjects.c:1010)
[ 249.268164][ T11] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 249.268313][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 249.268497][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 249.268651][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 249.268803][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 249.268944][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 249.269132][ 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)
[ 249.269247][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 249.269436][ T11] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 249.269586][ T11] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 249.269739][ T11] __dev_close_many (net/core/dev.c:1537 (discriminator 3))
[ 249.269881][ T11] ? __pfx___dev_close_many (net/core/dev.c:1525)
[ 249.270031][ T11] dev_close_many (net/core/dev.c:1588)
[ 249.270174][ T11] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 249.270319][ T11] ? ipv6_mc_down (net/ipv6/mcast.c:1140 net/ipv6/mcast.c:2777)
[ 249.270467][ T11] vlan_device_event (net/8021q/vlan.c:451)
[ 249.270622][ T11] ? __pfx_vlan_device_event (net/8021q/vlan.c:362)
[ 249.270769][ T11] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 249.270925][ T11] ? packet_notifier (net/packet/af_packet.c:4282)
[ 249.271095][ T11] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 249.271239][ T11] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 249.271384][ T11] dev_close_many (net/core/dev.c:1591)
[ 249.271529][ T11] ? fou_exit_net (net/ipv4/fou_core.c:1234)
[ 249.271683][ T11] ? __pfx_dev_close_many (net/core/dev.c:1578)
[ 249.271823][ T11] ? __pfx___mutex_trylock_common (kernel/locking/mutex.c:79)
[ 249.272000][ T11] unregister_netdevice_many_notify (net/core/dev.c:11545)
[ 249.272182][ T11] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11512)
[ 249.272362][ T11] ? default_device_exit_batch (net/core/dev.c:12103)
[ 249.272510][ 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)
[ 249.272653][ T11] ? rtnl_is_locked (net/core/rtnetlink.c:164)
[ 249.272808][ T11] ? unregister_netdevice_queue (net/core/dev.c:11497)
[ 249.272989][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 249.273164][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11496)
[ 249.273344][ T11] default_device_exit_batch (net/core/dev.c:12117)
[ 249.273486][ T11] ? __pfx_default_device_exit_batch (net/core/dev.c:12092)
[ 249.273663][ T11] ? ops_exit_list (net/core/net_namespace.c:171 (discriminator 3))
[ 249.273817][ T11] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 249.273961][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 249.274107][ T11] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 249.274251][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 249.274400][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 249.274543][ T11] ? process_one_work (kernel/workqueue.c:3205)
[ 249.274692][ T11] process_one_work (kernel/workqueue.c:3229)
[ 249.274841][ T11] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 249.274982][ T11] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 249.275125][ T11] ? assign_work (kernel/workqueue.c:1200)
[ 249.275275][ T11] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 249.275420][ T11] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 249.275644][ T11] kthread (kernel/kthread.c:389)
[ 249.275757][ T11] ? __pfx_kthread (kernel/kthread.c:342)
[ 249.275900][ T11] ret_from_fork (arch/x86/kernel/process.c:147)
[ 249.276055][ T11] ? __pfx_kthread (kernel/kthread.c:342)


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