======================================
| [   31.032209][  T246] dummy1: entered promiscuous mode
| [   31.032572][  T246] dummy2: entered promiscuous mode
| [   31.033197][    C1] BUG: spinlock bad magic on CPU#1, kworker/1:1/52
| [ 31.033397][ C1] lock: noop_qdisc+0x240/0x300, .magic: 00000000, .owner: kworker/1:1/52, .owner_cpu: 1 
[   31.034033][    C1] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   31.034334][    C1] Workqueue: events linkwatch_event
[   31.034482][    C1] Call Trace:
[   31.034601][    C1]  <IRQ>
[ 31.034697][ C1] dump_stack_lvl (lib/dump_stack.c:122) 
[ 31.034837][ C1] do_raw_spin_unlock (kernel/locking/spinlock_debug.c:100 kernel/locking/spinlock_debug.c:141) 
[ 31.034984][ C1] _raw_spin_unlock (./arch/x86/include/asm/preempt.h:94 ./include/linux/spinlock_api_smp.h:143 kernel/locking/spinlock.c:186) 
[ 31.035114][ C1] net_tx_action (./include/net/sch_generic.h:226 ./include/net/sch_generic.h:217 ./include/net/pkt_sched.h:128 ./include/net/pkt_sched.h:124 net/core/dev.c:5323) 
[ 31.035249][ C1] handle_softirqs (kernel/softirq.c:554) 
[ 31.035385][ C1] ? dev_deactivate_many (./include/linux/bottom_half.h:33 ./include/linux/netdevice.h:4448 net/sched/sch_generic.c:571 net/sched/sch_generic.c:1363) 
[ 31.035524][ C1] do_softirq (kernel/softirq.c:455 kernel/softirq.c:442) 
[   31.035625][    C1]  </IRQ>
[   31.035703][    C1]  <TASK>
[ 31.035767][ C1] __local_bh_enable_ip (kernel/softirq.c:382) 
[ 31.035908][ C1] dev_deactivate_many (net/sched/sch_generic.c:1356) 
[ 31.036051][ C1] ? __lock_release (kernel/locking/lockdep.c:5435) 
[ 31.036186][ C1] ? __linkwatch_run_queue (net/core/link_watch.c:234) 
[ 31.036342][ C1] dev_deactivate (./include/linux/list.h:111 ./include/linux/list.h:215 ./include/linux/list.h:229 net/sched/sch_generic.c:1398) 
[ 31.036477][ C1] ? __pfx_dev_deactivate (net/sched/sch_generic.c:1393) 
[ 31.036618][ C1] ? mark_held_locks (kernel/locking/lockdep.c:4273) 
[ 31.036759][ C1] linkwatch_do_dev (net/core/link_watch.c:177) 
[ 31.036885][ C1] __linkwatch_run_queue (./include/linux/spinlock.h:376 net/core/link_watch.c:236) 
[ 31.037028][ C1] ? __pfx___linkwatch_run_queue (net/core/link_watch.c:186) 
[ 31.037190][ C1] ? process_one_work (kernel/workqueue.c:3207) 
[ 31.037326][ C1] ? lock_acquire (kernel/locking/lockdep.c:5732) 
[ 31.037473][ C1] linkwatch_event (net/core/link_watch.c:278) 
[ 31.037600][ C1] process_one_work (kernel/workqueue.c:3231) 
[ 31.037735][ C1] ? __pfx___lock_release (kernel/locking/lockdep.c:5411) 
[ 31.037868][ C1] ? __pfx_process_one_work (kernel/workqueue.c:3133) 
[ 31.038000][ C1] ? assign_work (kernel/workqueue.c:1202) 
[ 31.038132][ C1] worker_thread (kernel/workqueue.c:3306 kernel/workqueue.c:3390) 
[ 31.038292][ C1] ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4299 kernel/locking/lockdep.c:4358) 
[ 31.038454][ C1] ? __pfx_worker_thread (kernel/workqueue.c:3339) 
[ 31.038601][ C1] ? __pfx_worker_thread (kernel/workqueue.c:3339) 
[ 31.038740][ C1] kthread (kernel/kthread.c:389) 
[ 31.038836][ C1] ? __pfx_kthread (kernel/kthread.c:342) 
[ 31.038974][ C1] ret_from_fork (arch/x86/kernel/process.c:147) 
[ 31.039111][ C1] ? __pfx_kthread (kernel/kthread.c:342) 


Finger prints:
do_raw_spin_unlock:_raw_spin_unlock:net_tx_action:handle_softirqs:do_softirq