======================================
| [ 22.702862][ T66] #3: ffffffffb3407e88 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12109)
| [ 22.703176][ T66] #4: ffffffffb33f6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   22.703487][   T66]
| [   22.703487][   T66] stack backtrace:
[   22.703945][   T66] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   22.704134][   T66] Workqueue: netns cleanup_net
[   22.704302][   T66] Call Trace:
[   22.704421][   T66]  <TASK>
[ 22.704501][ T66] dump_stack_lvl (lib/dump_stack.c:123)
[ 22.704661][ T66] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 22.704816][ T66] validate_chain (kernel/locking/lockdep.c:3894)
[ 22.704972][ T66] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 22.705126][ T66] ? 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)
[ 22.705279][ T66] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 22.705397][ T66] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 22.705556][ T66] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 22.705713][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 22.705903][ T66] ? find_held_lock (kernel/locking/lockdep.c:5339)
[ 22.706055][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 22.706210][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 22.706378][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 22.706531][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 22.706729][ T66] down_read (./arch/x86/include/asm/preempt.h:79 kernel/locking/rwsem.c:1246 kernel/locking/rwsem.c:1261 kernel/locking/rwsem.c:1526)
[ 22.706847][ T66] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 22.707040][ T66] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 22.707196][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4339 kernel/locking/lockdep.c:4406)
[ 22.707395][ T66] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 22.707550][ T66] __netdev_upper_dev_unlink (net/core/dev.c:8000 (discriminator 11) net/core/dev.c:8017 (discriminator 11) net/core/dev.c:8167 (discriminator 11))
[ 22.707706][ T66] ? __pfx___netdev_upper_dev_unlink (net/core/dev.c:8151)
[ 22.707893][ T66] ? find_held_lock (kernel/locking/lockdep.c:5339)
[ 22.708049][ T66] ? del_nbp (net/bridge/br_if.c:215 net/bridge/br_if.c:359)
[ 22.708165][ T66] ? 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)
[ 22.708320][ T66] netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 22.708473][ T66] ? __pfx_netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 22.708657][ T66] ? mutex_is_locked (./include/linux/instrumented.h:68 ./include/linux/atomic/atomic-instrumented.h:3188 kernel/locking/mutex.h:47 kernel/locking/mutex.c:66)
[ 22.708812][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 22.708967][ T66] del_nbp (net/bridge/br_if.c:365)
[ 22.709083][ T66] br_del_if (net/bridge/br_if.c:741)
[ 22.709202][ T66] br_device_event (net/bridge/br.c:141)
[ 22.709359][ T66] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 22.709512][ T66] ? packet_notifier (net/packet/af_packet.c:4282)
[ 22.709670][ T66] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 22.709826][ T66] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 22.709986][ T66] unregister_netdevice_many_notify (net/core/dev.c:11575)
[ 22.710177][ T66] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11516)
[ 22.710370][ T66] ? default_device_exit_batch (net/core/dev.c:12109)
[ 22.710528][ T66] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 22.710682][ T66] ? unregister_netdevice_queue (net/core/dev.c:11501)
[ 22.710869][ T66] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 22.711060][ T66] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 22.711251][ T66] default_device_exit_batch (net/core/dev.c:12123)
[ 22.711402][ T66] ? __pfx_default_device_exit_batch (net/core/dev.c:12098)
[ 22.711593][ T66] ? ops_exit_list (net/core/net_namespace.c:171 (discriminator 3))
[ 22.711752][ T66] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 22.711903][ T66] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 22.712058][ T66] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 22.712207][ T66] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 22.712360][ T66] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 22.712513][ T66] ? process_one_work (kernel/workqueue.c:3205)
[ 22.712667][ T66] process_one_work (kernel/workqueue.c:3229)
[ 22.712820][ T66] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 22.712976][ T66] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 22.713127][ T66] ? assign_work (kernel/workqueue.c:1200)
[ 22.713279][ T66] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 22.713427][ T66] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4347 kernel/locking/lockdep.c:4406)
[ 22.713701][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 22.713853][ T66] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 22.714008][ T66] kthread (kernel/kthread.c:389)
[ 22.714125][ T66] ? __pfx_kthread (kernel/kthread.c:342)
[ 22.714280][ T66] ret_from_fork (arch/x86/kernel/process.c:147)
[ 22.714434][ T66] ? __pfx_kthread (kernel/kthread.c:342)


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