======================================
| [ 2866.437235][ T11] #3: ffffffff8d007e88 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch (net/core/dev.c:12109)
| [ 2866.437545][ T11] #4: ffffffff8cff6a70 ((netdev_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
| [ 2866.437864][   T11]
| [ 2866.437864][   T11] stack backtrace:
[ 2866.438327][   T11] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 2866.438524][   T11] Workqueue: netns cleanup_net
[ 2866.438682][   T11] Call Trace:
[ 2866.438804][   T11]  <TASK>
[ 2866.438882][ T11] dump_stack_lvl (lib/dump_stack.c:123)
[ 2866.439040][ T11] print_deadlock_bug (kernel/locking/lockdep.c:3040)
[ 2866.439200][ T11] validate_chain (kernel/locking/lockdep.c:3894)
[ 2866.439353][ T11] ? __pfx_validate_chain (kernel/locking/lockdep.c:3860)
[ 2866.439516][ 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)
[ 2866.439670][ T11] ? mark_lock (kernel/locking/lockdep.c:4727 (discriminator 3))
[ 2866.439790][ T11] __lock_acquire (kernel/locking/lockdep.c:5226)
[ 2866.439951][ T11] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851)
[ 2866.440111][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 2866.440300][ T11] ? find_held_lock (kernel/locking/lockdep.c:5339)
[ 2866.440449][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 2866.440599][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 2866.440755][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 2866.440908][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 2866.441097][ 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)
[ 2866.441213][ T11] ? blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 2866.441408][ T11] ? __pfx_down_read (kernel/locking/rwsem.c:1522)
[ 2866.441561][ T11] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4339 kernel/locking/lockdep.c:4406)
[ 2866.441753][ T11] blocking_notifier_call_chain (kernel/notifier.c:380 kernel/notifier.c:368)
[ 2866.441912][ 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))
[ 2866.442071][ T11] ? __pfx___netdev_upper_dev_unlink (net/core/dev.c:8151)
[ 2866.442262][ T11] ? find_held_lock (kernel/locking/lockdep.c:5339)
[ 2866.442415][ T11] ? del_nbp (net/bridge/br_if.c:215 net/bridge/br_if.c:359)
[ 2866.442534][ 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)
[ 2866.442688][ T11] netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 2866.442845][ T11] ? __pfx_netdev_upper_dev_unlink (net/core/dev.c:8190)
[ 2866.443038][ 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)
[ 2866.443193][ T11] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 2866.443350][ T11] del_nbp (net/bridge/br_if.c:365)
[ 2866.443467][ T11] br_del_if (net/bridge/br_if.c:741)
[ 2866.443583][ T11] br_device_event (net/bridge/br.c:141)
[ 2866.443740][ T11] ? __pfx_br_device_event (net/bridge/br.c:29)
[ 2866.443894][ T11] ? packet_notifier (net/packet/af_packet.c:4282)
[ 2866.444048][ T11] notifier_call_chain (kernel/notifier.c:85 (discriminator 2))
[ 2866.444200][ T11] blocking_notifier_call_chain (kernel/notifier.c:381 kernel/notifier.c:368)
[ 2866.444353][ T11] unregister_netdevice_many_notify (net/core/dev.c:11575)
[ 2866.444544][ T11] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11516)
[ 2866.444734][ T11] ? default_device_exit_batch (net/core/dev.c:12109)
[ 2866.444890][ T11] ? rtnl_is_locked (net/core/rtnetlink.c:163)
[ 2866.445047][ T11] ? unregister_netdevice_queue (net/core/dev.c:11501)
[ 2866.445236][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 2866.445430][ T11] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11500)
[ 2866.445622][ T11] default_device_exit_batch (net/core/dev.c:12123)
[ 2866.445779][ T11] ? __pfx_default_device_exit_batch (net/core/dev.c:12098)
[ 2866.445992][ T11] ? ops_exit_list (net/core/net_namespace.c:171 (discriminator 3))
[ 2866.446152][ T11] cleanup_net (net/core/net_namespace.c:647 (discriminator 3))
[ 2866.446309][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5814)
[ 2866.446466][ T11] ? __pfx_cleanup_net (net/core/net_namespace.c:592)
[ 2866.446621][ T11] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 37))
[ 2866.446779][ T11] ? lock_acquire (kernel/locking/lockdep.c:5822)
[ 2866.446939][ T11] ? process_one_work (kernel/workqueue.c:3205)
[ 2866.447096][ T11] process_one_work (kernel/workqueue.c:3229)
[ 2866.447258][ T11] ? __pfx___lock_release (kernel/locking/lockdep.c:5501)
[ 2866.447425][ T11] ? __pfx_process_one_work (kernel/workqueue.c:3131)
[ 2866.447582][ T11] ? assign_work (kernel/workqueue.c:1200)
[ 2866.447736][ T11] worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391)
[ 2866.447891][ T11] ? __pfx_worker_thread (kernel/workqueue.c:3337)
[ 2866.448044][ T11] kthread (kernel/kthread.c:389)
[ 2866.448164][ T11] ? __pfx_kthread (kernel/kthread.c:342)
[ 2866.448317][ T11] ret_from_fork (arch/x86/kernel/process.c:147)
[ 2866.448474][ T11] ? __pfx_kthread (kernel/kthread.c:342)


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