======================================
| [ 59.250925][ T10] ret_from_fork_asm (arch/x86/entry/entry_64.S:256) 
| [   59.251144][   T10]
| [   59.251219][   T10]
| [   59.251219][   T10] stack backtrace:
[   59.251629][   T10] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   59.252118][   T10] Workqueue: netns cleanup_net
[   59.252287][   T10] Call Trace:
[   59.252402][   T10]  <TASK>
[ 59.252478][ T10] dump_stack_lvl (lib/dump_stack.c:117) 
[ 59.252623][ T10] print_bad_irq_dependency (kernel/locking/lockdep.c:2626) 
[ 59.252797][ T10] ? __pfx_print_bad_irq_dependency (kernel/locking/lockdep.c:2569) 
[ 59.252989][ T10] ? __pfx_usage_skip (kernel/locking/lockdep.c:2264) 
[ 59.253221][ T10] ? __bfs (kernel/locking/lockdep.c:1787) 
[ 59.253340][ T10] ? __pfx_usage_match (kernel/locking/lockdep.c:2256) 
[ 59.253489][ T10] check_irq_usage (kernel/locking/lockdep.c:2871) 
[ 59.253642][ T10] ? arch_stack_walk (arch/x86/kernel/stacktrace.c:24) 
[ 59.253871][ T10] ? __pfx_check_irq_usage (kernel/locking/lockdep.c:2790) 
[ 59.254024][ T10] ? __bfs (kernel/locking/lockdep.c:1787) 
[ 59.254138][ T10] ? __pfx_hlock_conflict (kernel/locking/lockdep.c:2016) 
[ 59.254289][ T10] ? check_path.constprop.0 (kernel/locking/lockdep.c:2145) 
[ 59.254436][ T10] ? check_noncircular (kernel/locking/lockdep.c:2172) 
[ 59.254590][ T10] ? __pfx_check_noncircular (kernel/locking/lockdep.c:2163) 
[ 59.254810][ T10] ? find_held_lock (kernel/locking/lockdep.c:5244) 
[ 59.254962][ T10] ? check_prev_add (kernel/locking/lockdep.c:3138) 
[ 59.255110][ T10] check_prev_add (kernel/locking/lockdep.c:3138) 
[ 59.255263][ T10] ? validate_chain (./include/linux/hash.h:78 kernel/locking/lockdep.c:3759 kernel/locking/lockdep.c:3782 kernel/locking/lockdep.c:3837) 
[ 59.255495][ T10] validate_chain (kernel/locking/lockdep.c:3254 kernel/locking/lockdep.c:3869) 
[ 59.255727][ T10] ? mark_lock (kernel/locking/lockdep.c:4656 (discriminator 3)) 
[ 59.255850][ T10] ? __pfx_validate_chain (kernel/locking/lockdep.c:3825) 
[ 59.256003][ T10] ? 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) 
[ 59.256151][ T10] ? mark_lock (kernel/locking/lockdep.c:4656 (discriminator 3)) 
[ 59.256264][ T10] __lock_acquire (kernel/locking/lockdep.c:5137) 
[ 59.256414][ T10] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5756) 
[ 59.256557][ T10] ? __get_task_comm (fs/exec.c:1234) 
[ 59.256785][ T10] ? mark_lock (kernel/locking/lockdep.c:4656 (discriminator 3)) 
[ 59.256892][ T10] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5719) 
[ 59.257035][ T10] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 52)) 
[ 59.257178][ T10] ? __get_task_comm (fs/exec.c:1234) 
[ 59.257321][ T10] ? lock_acquire (kernel/locking/lockdep.c:5727) 
[ 59.257473][ T10] ? __get_task_comm (fs/exec.c:1234) 
[ 59.257698][ T10] _raw_spin_lock (./include/linux/spinlock_api_smp.h:134 kernel/locking/spinlock.c:154) 
[ 59.257842][ T10] ? __get_task_comm (fs/exec.c:1234) 
[ 59.257998][ T10] __get_task_comm (fs/exec.c:1234) 
[ 59.258140][ T10] ref_tracker_alloc (lib/ref_tracker.c:217) 
[ 59.258285][ T10] ? lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5756) 
[ 59.258429][ T10] ? __pfx_ref_tracker_alloc (lib/ref_tracker.c:193) 
[ 59.258574][ T10] ? rt_flush_dev (./include/linux/netdevice.h:4036 ./include/linux/netdevice.h:4114 net/ipv4/route.c:1555) 
[ 59.258717][ T10] ? fib_netdev_event (net/ipv4/fib_frontend.c:1520) 
[ 59.258928][ T10] ? notifier_call_chain (kernel/notifier.c:93 (discriminator 2)) 
[ 59.259070][ T10] ? unregister_netdevice_many_notify (net/core/dev.c:11171) 
[ 59.259247][ T10] ? default_device_exit_batch (net/core/dev.c:11707) 
[ 59.259429][ T10] ? cleanup_net (net/core/net_namespace.c:636 (discriminator 3)) 
[ 59.259639][ T10] ? process_one_work (kernel/workqueue.c:3254) 
[ 59.259779][ T10] ? worker_thread (kernel/workqueue.c:3329 kernel/workqueue.c:3416) 
[ 59.259922][ T10] ? kthread (kernel/kthread.c:388) 
[ 59.260028][ T10] ? ret_from_fork (arch/x86/kernel/process.c:147) 
[ 59.260196][ T10] ? ret_from_fork_asm (arch/x86/entry/entry_64.S:256) 
[ 59.260410][ T10] ? do_raw_spin_lock (./arch/x86/include/asm/atomic.h:115 ./include/linux/atomic/atomic-arch-fallback.h:2170 ./include/linux/atomic/atomic-instrumented.h:1302 ./include/asm-generic/qspinlock.h:111 kernel/locking/spinlock_debug.c:116) 
[ 59.260558][ T10] ? __pfx_do_raw_spin_lock (kernel/locking/spinlock_debug.c:114) 
[ 59.260700][ T10] ? lock_acquire (kernel/locking/lockdep.c:5727) 
[ 59.260842][ T10] ? rt_flush_dev (net/ipv4/route.c:1551) 
[ 59.261062][ T10] rt_flush_dev (./include/linux/netdevice.h:4036 ./include/linux/netdevice.h:4114 net/ipv4/route.c:1555) 
[ 59.261207][ T10] ? __timer_delete_sync (kernel/time/timer.c:1648 (discriminator 1)) 
[ 59.261363][ T10] ? __timer_delete_sync (kernel/time/timer.c:1668 (discriminator 34)) 
[ 59.261507][ T10] fib_netdev_event (net/ipv4/fib_frontend.c:1520) 
[ 59.261718][ T10] notifier_call_chain (kernel/notifier.c:93 (discriminator 2)) 
[ 59.261878][ T10] unregister_netdevice_many_notify (net/core/dev.c:11171) 
[ 59.262055][ T10] ? 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.c:81 kernel/locking/mutex.c:91) 
[ 59.262201][ T10] ? __pfx_unregister_netdevice_many_notify (net/core/dev.c:11113) 
[ 59.262457][ T10] ? __pfx_unregister_netdevice_queue (net/core/dev.c:11097) 
[ 59.262635][ T10] default_device_exit_batch (net/core/dev.c:11707) 
[ 59.262777][ T10] ? __pfx_default_device_exit_batch (net/core/dev.c:11682) 
[ 59.262952][ T10] ? ops_exit_list (net/core/net_namespace.c:169 (discriminator 3)) 
[ 59.263192][ T10] cleanup_net (net/core/net_namespace.c:636 (discriminator 3)) 
[ 59.263332][ T10] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5719) 
[ 59.263475][ T10] ? __pfx_cleanup_net (net/core/net_namespace.c:581) 
[ 59.263616][ T10] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 52)) 
[ 59.263827][ T10] ? process_one_work (kernel/workqueue.c:3230) 
[ 59.263970][ T10] ? lock_acquire (kernel/locking/lockdep.c:5727) 
[ 59.264111][ T10] ? process_one_work (kernel/workqueue.c:3230) 
[ 59.264261][ T10] process_one_work (kernel/workqueue.c:3254) 
[ 59.264465][ T10] ? __pfx___lock_release (kernel/locking/lockdep.c:5406) 
[ 59.264618][ T10] ? __pfx_process_one_work (kernel/workqueue.c:3156) 
[ 59.264764][ T10] ? assign_work (kernel/workqueue.c:1209) 
[ 59.264907][ T10] worker_thread (kernel/workqueue.c:3329 kernel/workqueue.c:3416) 
[ 59.265054][ T10] ? __pfx_worker_thread (kernel/workqueue.c:3362) 
[ 59.265197][ T10] kthread (kernel/kthread.c:388) 
[ 59.265304][ T10] ? __pfx_kthread (kernel/kthread.c:341) 
[ 59.265446][ T10] ret_from_fork (arch/x86/kernel/process.c:147) 
[ 59.265589][ T10] ? __pfx_kthread (kernel/kthread.c:341) 


Finger prints:
ret_from_fork_asm:dump_stack_lvl:print_bad_irq_dependency:check_irq_usage