======================================
| [ 30.951552][ T11] #3: ffffffffb99f1088 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12109)
| [ 30.951886][ T11] #4: ffffffffb99dfc30 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [   30.952221][   T11]
| [   30.952221][   T11] stack backtrace:
[   30.952709][   T11] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   30.952908][   T11] Workqueue: netns cleanup_net
[   30.953082][   T11] Call Trace:
[   30.953220][   T11]  <TASK>
[ 30.953309][ T11] dump_stack_lvl (lib/dump_stack.c:123)
[ 30.953484][ T11] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 30.953647][ T11] validate_chain (kernel/locking/lockdep.c:3894)
[ 30.953819][ T11] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 30.953988][ 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)
[ 30.954155][ T11] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 30.954280][ T11] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 30.954463][ T11] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 30.954627][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 30.954837][ T11] ? find_held_lock (kernel/locking/lockdep.c:5339)
[ 30.955001][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 30.955168][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 30.955343][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 30.955505][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 30.955712][ 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)
[ 30.955840][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 30.956043][ T11] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 30.956213][ T11] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4339 kernel/locking/lockdep.c:4406)
[ 30.956419][ T11] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 30.956584][ T11] __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))
[ 30.956751][ T11] ? __pfx___netdev_upper_dev_unlink (net/core/dev.c:8151)
[ 30.956967][ T11] ? find_held_lock (kernel/locking/lockdep.c:5339)
[ 30.957133][ T11] ? del_nbp (net/bridge/br_if.c:215 net/bridge/br_if.c:359) bridge
[ 30.957334][ 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)
[ 30.957500][ T11] netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 30.957664][ T11] ? __pfx_netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 30.957874][ T11] ? mutex_spin_on_owner (kernel/locking/mutex.c:353)
[ 30.958040][ T11] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 30.958220][ T11] del_nbp (net/bridge/br_if.c:365) bridge
[ 30.958414][ T11] br_del_if (net/bridge/br_if.c:741) bridge
[ 30.958614][ T11] br_device_event (net/bridge/br.c:141) bridge
[ 30.958807][ T11] ? __pfx_br_device_event (net/bridge/br.c:29) bridge
[ 30.959035][ T11] ? netconsole_netdev_event (drivers/net/netconsole.c:1082)
[ 30.959201][ T11] ? packet_notifier (net/packet/af_packet.c:4282)
[ 30.959370][ T11] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 30.959562][ T11] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 30.959729][ T11] unregister_netdevice_many_notify (net/core/dev.c:11575)
[ 30.959938][ T11] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11516)
[ 30.960144][ T11] ? default_device_exit_batch (net/core/dev.c:12109)
[ 30.960310][ T11] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 30.960475][ T11] ? unregister_netdevice_queue (net/core/dev.c:11501)
[ 30.960681][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 30.960917][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 30.961123][ T11] default_device_exit_batch (net/core/dev.c:12123)
[ 30.961287][ T11] ? __pfx_default_device_exit_batch (net/core/dev.c:12098)
[ 30.961507][ 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)
[ 30.961672][ T11] ? 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)
[ 30.961896][ T11] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 30.962068][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 30.962235][ T11] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 30.962412][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 30.962578][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 30.962744][ T11] ? process_one_work (kernel/workqueue.c:3205)
[ 30.962921][ T11] process_one_work (kernel/workqueue.c:3229)
[ 30.963092][ T11] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 30.963259][ T11] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 30.963426][ T11] ? assign_work (kernel/workqueue.c:1200)
[ 30.963588][ T11] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 30.963754][ T11] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 30.963915][ T11] kthread (kernel/kthread.c:389)
[ 30.964041][ T11] ? __pfx_kthread (kernel/kthread.c:342)
[ 30.964202][ T11] ret_from_fork (arch/x86/kernel/process.c:147)
[ 30.964365][ T11] ? __pfx_kthread (kernel/kthread.c:342)


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