======================================
| [ 1176.157037][ T11] #3: ffffffff8ac07e88 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12109)
| [ 1176.157348][ T11] #4: ffffffff8abf6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [ 1176.157657][   T11]
| [ 1176.157657][   T11] stack backtrace:
[ 1176.158115][   T11] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 1176.158305][   T11] Workqueue: netns cleanup_net
[ 1176.158466][   T11] Call Trace:
[ 1176.158585][   T11]  <TASK>
[ 1176.158667][ T11] dump_stack_lvl (lib/dump_stack.c:123)
[ 1176.158827][ T11] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 1176.158982][ T11] validate_chain (kernel/locking/lockdep.c:3894)
[ 1176.159139][ T11] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 1176.159299][ 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)
[ 1176.159451][ T11] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 1176.159568][ T11] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 1176.159723][ T11] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 1176.159877][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 1176.160068][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 1176.160219][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 1176.160377][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 1176.160529][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 1176.160723][ 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)
[ 1176.160843][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 1176.161038][ T11] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 1176.161194][ T11] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 1176.161347][ T11] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 1176.161506][ 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))
[ 1176.161660][ T11] ? __pfx___netdev_upper_dev_unlink (net/core/dev.c:8151)
[ 1176.161851][ T11] ? find_held_lock (kernel/locking/lockdep.c:5339)
[ 1176.162006][ T11] ? del_nbp (net/bridge/br_if.c:215 net/bridge/br_if.c:359)
[ 1176.162123][ 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)
[ 1176.162275][ T11] netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 1176.162432][ T11] ? __pfx_netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 1176.162622][ T11] ? 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)
[ 1176.162775][ T11] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 1176.162930][ T11] del_nbp (net/bridge/br_if.c:365)
[ 1176.163051][ T11] br_del_if (net/bridge/br_if.c:741)
[ 1176.163171][ T11] br_device_event (net/bridge/br.c:141)
[ 1176.163327][ T11] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 1176.163484][ T11] ? packet_notifier (net/packet/af_packet.c:4282)
[ 1176.163647][ T11] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 1176.163805][ T11] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 1176.163959][ T11] unregister_netdevice_many_notify (net/core/dev.c:11575)
[ 1176.164153][ T11] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11516)
[ 1176.164344][ T11] ? default_device_exit_batch (net/core/dev.c:12109)
[ 1176.164497][ T11] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 1176.164654][ T11] ? unregister_netdevice_queue (net/core/dev.c:11501)
[ 1176.164845][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 1176.165037][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 1176.165225][ T11] default_device_exit_batch (net/core/dev.c:12123)
[ 1176.165376][ T11] ? __pfx_default_device_exit_batch (net/core/dev.c:12098)
[ 1176.165569][ T11] ? ops_exit_list (net/core/net_namespace.c:171 (discriminator 3))
[ 1176.165730][ T11] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 1176.165882][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 1176.166036][ T11] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 1176.166187][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 1176.166339][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 1176.166490][ T11] ? process_one_work (kernel/workqueue.c:3205)
[ 1176.166647][ T11] process_one_work (kernel/workqueue.c:3229)
[ 1176.166800][ T11] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 1176.166962][ T11] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 1176.167116][ T11] ? assign_work (kernel/workqueue.c:1200)
[ 1176.167287][ T11] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 1176.167443][ T11] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 1176.167594][ T11] kthread (kernel/kthread.c:389)
[ 1176.167712][ T11] ? __pfx_kthread (kernel/kthread.c:342)
[ 1176.167867][ T11] ret_from_fork (arch/x86/kernel/process.c:147)
[ 1176.168027][ T11] ? __pfx_kthread (kernel/kthread.c:342)


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