======================================
| [ 558.939383][ C2] ret_from_fork_asm (arch/x86/entry/entry_64.S:258) 
| [  558.939385][    C2]
| [  558.939385][    C2]
| [  558.939385][    C2] stack backtrace:
[  558.939396][    C2] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  558.939401][    C2] Workqueue: events_unbound flush_to_ldisc
[  558.939407][    C2] Call Trace:
[  558.939411][    C2]  <IRQ>
[ 558.939415][ C2] dump_stack_lvl (lib/dump_stack.c:123) 
[ 558.939420][ C2] print_irq_inversion_bug.part.0 (kernel/locking/lockdep.c:4127) 
[ 558.939425][ C2] mark_lock_irq (kernel/locking/lockdep.c:4295) 
[ 558.939431][ C2] mark_lock (kernel/locking/lockdep.c:4753) 
[ 558.939435][ C2] mark_usage (kernel/locking/lockdep.c:4639) 
[ 558.939437][ C2] __lock_acquire (kernel/locking/lockdep.c:5191) 
[ 558.939442][ C2] lock_acquire.part.0 (kernel/locking/lockdep.c:470 kernel/locking/lockdep.c:5870) 
[ 558.939445][ C2] ? console_lock_spinning_enable (kernel/printk/printk.c:1924) 
[ 558.939449][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 558.939456][ C2] ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831) 
[ 558.939458][ C2] ? console_lock_spinning_enable (kernel/printk/printk.c:1924) 
[ 558.939463][ C2] console_lock_spinning_enable (kernel/printk/printk.c:1925) 
[ 558.939466][ C2] ? console_lock_spinning_enable (kernel/printk/printk.c:1924) 
[ 558.939469][ C2] console_emit_next_record (kernel/printk/printk.c:3050 (discriminator 3) kernel/printk/printk.c:3137 (discriminator 3)) 
[ 558.939473][ C2] ? devkmsg_read (kernel/printk/printk.c:3082) 
[ 558.939477][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 558.939482][ C2] console_flush_all (kernel/printk/printk.c:3227) 
[ 558.939487][ C2] ? console_emit_next_record (kernel/printk/printk.c:3188) 
[ 558.939490][ C2] ? __lock_acquire (kernel/locking/lockdep.c:5237) 
[ 558.939495][ C2] console_unlock (kernel/printk/printk.c:3286 kernel/printk/printk.c:3325) 
[ 558.939498][ C2] ? console_flush_all (kernel/printk/printk.c:3320) 
[ 558.939502][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 558.939505][ C2] ? irq_work_single (kernel/irq_work.c:222) 
[ 558.939508][ C2] ? irq_work_single (kernel/irq_work.c:222) 
[ 558.939513][ C2] wake_up_klogd_work_func (kernel/printk/printk.c:4529) 
[ 558.939516][ C2] irq_work_single (kernel/irq_work.c:222) 
[ 558.939520][ C2] irq_work_run_list (kernel/irq_work.c:251 (discriminator 3)) 
[ 558.939523][ C2] ? irq_work_tick (kernel/irq_work.c:277) 
[ 558.939526][ C2] update_process_times (kernel/time/timer.c:2478) 
[ 558.939530][ C2] tick_nohz_handler (kernel/time/tick-sched.c:277 kernel/time/tick-sched.c:297) 
[ 558.939533][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 558.939537][ C2] __run_hrtimer (kernel/time/hrtimer.c:1761) 
[ 558.939541][ C2] ? tick_do_update_jiffies64.part.0 (kernel/time/tick-sched.c:285) 
[ 558.939545][ C2] __hrtimer_run_queues (./include/linux/timerqueue.h:25 kernel/time/hrtimer.c:1805) 
[ 558.939549][ C2] ? hrtimer_interrupt (kernel/time/hrtimer.c:640 (discriminator 2) kernel/time/hrtimer.c:1869 (discriminator 2)) 
[ 558.939553][ C2] ? __run_hrtimer (kernel/time/hrtimer.c:1795) 
[ 558.939556][ C2] ? kvm_clock_get_cycles (./arch/x86/include/asm/preempt.h:95 arch/x86/kernel/kvmclock.c:80 arch/x86/kernel/kvmclock.c:86) 
[ 558.939563][ C2] hrtimer_interrupt (kernel/time/hrtimer.c:1890) 
[ 558.939567][ C2] ? __common_interrupt (./include/asm-generic/irq_regs.h:28 arch/x86/kernel/irq.c:328) 
[ 558.939576][ C2] __sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1057) 
[ 558.939579][ C2] sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1050 arch/x86/kernel/apic/apic.c:1050) 
[  558.939583][    C2]  </IRQ>
[  558.939584][    C2]  <TASK>
[ 558.939585][ C2] asm_sysvec_apic_timer_interrupt (./arch/x86/include/asm/idtentry.h:702) 
[ 558.939588][ C2] RIP: 0010:_raw_spin_unlock_irqrestore (./include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:194) 
[ 558.939592][ C2] Code: 74 24 10 e8 31 ba f9 fd 48 89 ef e8 59 09 fa fd 81 e3 00 02 00 00 75 25 9c 58 f6 c4 02 75 2d 48 85 db 74 01 fb bf 01 00 00 00 <e8> 9a 3d ee fd 65 8b 05 13 5c 03 02 85 c0 74 0a 5b 5d c3 e8 d7 be
All code
========
   0:	74 24                	je     0x26
   2:	10 e8                	adc    %ch,%al
   4:	31 ba f9 fd 48 89    	xor    %edi,-0x76b70207(%rdx)
   a:	ef                   	out    %eax,(%dx)
   b:	e8 59 09 fa fd       	call   0xfffffffffdfa0969
  10:	81 e3 00 02 00 00    	and    $0x200,%ebx
  16:	75 25                	jne    0x3d
  18:	9c                   	pushf
  19:	58                   	pop    %rax
  1a:	f6 c4 02             	test   $0x2,%ah
  1d:	75 2d                	jne    0x4c
  1f:	48 85 db             	test   %rbx,%rbx
  22:	74 01                	je     0x25
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
  2a:*	e8 9a 3d ee fd       	call   0xfffffffffdee3dc9		<-- trapping instruction
  2f:	65 8b 05 13 5c 03 02 	mov    %gs:0x2035c13(%rip),%eax        # 0x2035c49
  36:	85 c0                	test   %eax,%eax
  38:	74 0a                	je     0x44
  3a:	5b                   	pop    %rbx
  3b:	5d                   	pop    %rbp
  3c:	c3                   	ret
  3d:	e8                   	.byte 0xe8
  3e:	d7                   	xlat   %ds:(%rbx)
  3f:	be                   	.byte 0xbe

Code starting with the faulting instruction
===========================================
   0:	e8 9a 3d ee fd       	call   0xfffffffffdee3d9f
   5:	65 8b 05 13 5c 03 02 	mov    %gs:0x2035c13(%rip),%eax        # 0x2035c1f
   c:	85 c0                	test   %eax,%eax
   e:	74 0a                	je     0x1a
  10:	5b                   	pop    %rbx
  11:	5d                   	pop    %rbp
  12:	c3                   	ret
  13:	e8                   	.byte 0xe8
  14:	d7                   	xlat   %ds:(%rbx)
  15:	be                   	.byte 0xbe
[  558.939595][    C2] RSP: 0018:ffffc90000787a68 EFLAGS: 00000206
[  558.939601][    C2] RAX: 0000000000000006 RBX: 0000000000000200 RCX: 0000000000000080
[  558.939603][    C2] RDX: 0000000000000000 RSI: ffffffffac7ea7a3 RDI: 0000000000000001
[  558.939605][    C2] RBP: ffffffffaf067760 R08: 0000000000000001 R09: 0000000000000001
[  558.939606][    C2] R10: ffffffffad61c117 R11: ffff888005fb0970 R12: ffffffffaf067868
[  558.939608][    C2] R13: 00000000ffffffff R14: 0000000000000286 R15: ffffffffaf0678a0
[ 558.939615][ C2] uart_start (drivers/tty/serial/serial_core.c:74 drivers/tty/serial/serial_core.c:92 drivers/tty/serial/serial_core.c:88 drivers/tty/serial/serial_core.c:174) 
[ 558.939619][ C2] __receive_buf (drivers/tty/n_tty.c:1631) 
[ 558.939625][ C2] n_tty_receive_buf_common (drivers/tty/n_tty.c:1725) 
[ 558.939632][ C2] tty_port_default_receive_buf (drivers/tty/tty_port.c:39) 
[ 558.939636][ C2] flush_to_ldisc (drivers/tty/tty_buffer.c:445 drivers/tty/tty_buffer.c:495) 
[ 558.939641][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 558.939646][ C2] process_one_work (kernel/workqueue.c:3241) 
[ 558.939652][ C2] ? pwq_dec_nr_in_flight (kernel/workqueue.c:3138) 
[ 558.939658][ C2] ? assign_work (kernel/workqueue.c:1204) 
[ 558.939662][ C2] worker_thread (kernel/workqueue.c:3313 kernel/workqueue.c:3400) 
[ 558.939668][ C2] ? rescuer_thread (kernel/workqueue.c:3346) 
[ 558.939672][ C2] kthread (kernel/kthread.c:463) 
[ 558.939676][ C2] ? kthread_is_per_cpu (kernel/kthread.c:412) 
[ 558.939679][ C2] ? ret_from_fork (arch/x86/kernel/process.c:147) 
[ 558.939681][ C2] ? __lock_release (kernel/locking/lockdep.c:5536) 
[ 558.939684][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 558.939688][ C2] ? kthread_is_per_cpu (kernel/kthread.c:412) 
[ 558.939692][ C2] ret_from_fork (arch/x86/kernel/process.c:154) 
[ 558.939694][ C2] ? kthread_is_per_cpu (kernel/kthread.c:412) 


Finger prints:
ret_from_fork_asm:dump_stack_lvl:mark_lock_irq:mark_lock:mark_usage