======================================
| [   15.423616][   T12]  #5: ff1100000ff11e10 (&dev_instance_lock_key){+.+.}-{4:4}, at: unregister_netdevice_many_notify (./include/linux/netdevice.h:2861 net/core/dev.c:12578)
| [   15.423872][   T12]
| [   15.423872][   T12] stack backtrace:
| [   15.424022][   T12] Tainted: [W]=WARN
[   15.424023][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   15.424024][   T12] Workqueue: netns cleanup_net
[   15.424028][   T12] Call Trace:
[   15.424029][   T12]  <TASK>
[   15.424031][   T12]  dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
[   15.424034][   T12]  print_circular_bug.cold (kernel/locking/lockdep.c:2087)
[   15.424037][   T12]  check_noncircular (kernel/locking/lockdep.c:2219)
[   15.424041][   T12]  check_prev_add (kernel/locking/lockdep.c:3209)
[   15.424042][   T12]  ? lock_acquire.part.0 (kernel/locking/lockdep.c:5942 (discriminator 2))
[   15.424045][   T12]  validate_chain (kernel/locking/lockdep.c:3328 kernel/locking/lockdep.c:3952)
[   15.424047][   T12]  __lock_acquire (kernel/locking/lockdep.c:5288)
[   15.424050][   T12]  lock_acquire.part.0 (kernel/locking/lockdep.c:5942 (discriminator 2))
[   15.424051][   T12]  ? unregister_netdevice_many_notify (./include/linux/netdevice.h:2861 net/core/dev.c:12578)
[   15.424053][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 3) kernel/rcu/tree.c:753 (discriminator 3))
[   15.424056][   T12]  ? lock_acquire (./include/trace/events/lock.h:23 (discriminator 22) kernel/locking/lockdep.c:5905 (discriminator 22))
[   15.424058][   T12]  __mutex_lock (kernel/locking/mutex.c:646 kernel/locking/mutex.c:821)
[   15.424060][   T12]  ? unregister_netdevice_many_notify (./include/linux/netdevice.h:2861 net/core/dev.c:12578)
[   15.424061][   T12]  ? unregister_netdevice_many_notify (./include/linux/netdevice.h:2861 net/core/dev.c:12578)
[   15.424063][   T12]  ? __lock_acquire (kernel/locking/lockdep.c:5288)
[   15.424065][   T12]  ? ww_mutex_lock (kernel/locking/mutex.c:934)
[   15.424066][   T12]  ? find_held_lock (kernel/locking/lockdep.c:5401)
[   15.424068][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 3) kernel/rcu/tree.c:753 (discriminator 3))
[   15.424069][   T12]  ? mark_held_locks (kernel/locking/lockdep.c:4369)
[   15.424071][   T12]  ? kfree (mm/slub.c:6787 (discriminator 1))
[   15.424074][   T12]  ? lockdep_hardirqs_on_prepare.part.0 (kernel/locking/lockdep.c:470 (discriminator 2) kernel/locking/lockdep.c:4455 (discriminator 2))
[   15.424076][   T12]  ? _raw_spin_unlock_irqrestore (./include/linux/spinlock_api_smp.h:210 (discriminator 6) kernel/locking/spinlock.c:221 (discriminator 6))
[   15.424079][   T12]  ? unregister_netdevice_many_notify (./include/linux/netdevice.h:2861 net/core/dev.c:12578)
[   15.424080][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   15.424082][   T12]  unregister_netdevice_many_notify (./include/linux/netdevice.h:2861 net/core/dev.c:12578)
[   15.424083][   T12]  ? ops_undo_list (net/core/net_namespace.c:206 net/core/net_namespace.c:253)
[   15.424085][   T12]  ? worker_thread (kernel/workqueue.c:3479 kernel/workqueue.c:3560)
[   15.424086][   T12]  ? kthread (kernel/kthread.c:436)
[   15.424088][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:158)
[   15.424089][   T12]  ? ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
[   15.424091][   T12]  ? unregister_netdevice_queued (./include/linux/list.h:419 (discriminator 3))
[   15.424093][   T12]  ? unregister_netdevice_many (net/core/dev.c:12690)
[   15.424095][   T12]  default_device_exit_batch (net/core/dev.c:12690 net/core/dev.c:13390)
[   15.424097][   T12]  ? unregister_netdevice_queue (./include/linux/list.h:173)
[   15.424099][   T12]  ? perf_trace_sched_switch (./include/linux/list.h:1037 (discriminator 3))
[   15.424101][   T12]  ? fou_exit_net (net/ipv4/fou_core.c:1228)
[   15.424104][   T12]  ops_undo_list (net/core/net_namespace.c:206 net/core/net_namespace.c:253)
[   15.424106][   T12]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4516)
[   15.424109][   T12]  ? netns_install (./include/linux/ns_common.h:26)
[   15.424110][   T12]  ? __lock_release.isra.0 (kernel/locking/lockdep.c:5588)
[   15.424112][   T12]  ? idr_destroy (lib/radix-tree.c:310 lib/radix-tree.c:674 lib/radix-tree.c:1563)
[   15.424115][   T12]  cleanup_net (net/core/net_namespace.c:706)
[   15.424117][   T12]  ? net_passive_dec (./include/linux/llist.h:241)
[   15.424119][   T12]  ? lock_acquire (./include/trace/events/lock.h:23 (discriminator 22) kernel/locking/lockdep.c:5905 (discriminator 22))
[   15.424121][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 3) kernel/rcu/tree.c:753 (discriminator 3))
[   15.424123][   T12]  process_one_work (kernel/workqueue.c:3396)
[   15.424125][   T12]  ? __queue_delayed_work (kernel/workqueue.c:2622)
[   15.424126][   T12]  ? lock_acquire.part.0 (kernel/locking/lockdep.c:5942 (discriminator 2))
[   15.424129][   T12]  worker_thread (kernel/workqueue.c:3479 kernel/workqueue.c:3560)
[   15.424132][   T12]  ? rescuer_thread (./include/linux/list.h:419 (discriminator 3))
[   15.424133][   T12]  kthread (kernel/kthread.c:436)
[   15.424135][   T12]  ? trace_irq_enable.constprop.0 (./include/trace/events/preemptirq.h:40 (discriminator 22))
[   15.424138][   T12]  ? kthread_affine_preferred (kernel/kthread.c:857)
[   15.424140][   T12]  ret_from_fork (arch/x86/kernel/process.c:158)
[   15.424141][   T12]  ? arch_exit_to_user_mode_prepare.isra.0 (arch/x86/entry/vdso/vma.c:80 (discriminator 1))
[   15.424143][   T12]  ? __switch_to (arch/x86/kernel/process_64.c:403 arch/x86/kernel/process_64.c:663)
[   15.424146][   T12]  ? kthread_affine_preferred (kernel/kthread.c:857)


Finger prints:
check_prev_add:validate_chain:__lock_acquire:__mutex_lock:unregister_netdevice_many_notify