======================================
| [ 621.590709][ C2] ret_from_fork_asm (arch/x86/entry/entry_64.S:258) 
| [  621.590711][    C2]
| [  621.590712][    C2]
| [  621.590712][    C2] stack backtrace:
[  621.590720][    C2] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  621.590723][    C2] Workqueue: events_unbound flush_to_ldisc
[  621.590729][    C2] Call Trace:
[  621.590731][    C2]  <IRQ>
[ 621.590736][ C2] dump_stack_lvl (lib/dump_stack.c:123) 
[ 621.590742][ C2] print_irq_inversion_bug.part.0 (kernel/locking/lockdep.c:4127) 
[ 621.590747][ C2] mark_lock_irq (kernel/locking/lockdep.c:4295) 
[ 621.590753][ C2] mark_lock (kernel/locking/lockdep.c:4753) 
[ 621.590757][ C2] mark_usage (kernel/locking/lockdep.c:4639) 
[ 621.590760][ C2] __lock_acquire (kernel/locking/lockdep.c:5191) 
[ 621.590764][ C2] lock_acquire.part.0 (kernel/locking/lockdep.c:470 kernel/locking/lockdep.c:5870) 
[ 621.590767][ C2] ? console_lock_spinning_enable (kernel/printk/printk.c:1924) 
[ 621.590771][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 621.590778][ C2] ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831) 
[ 621.590780][ C2] ? console_lock_spinning_enable (kernel/printk/printk.c:1924) 
[ 621.590784][ C2] console_lock_spinning_enable (kernel/printk/printk.c:1925) 
[ 621.590787][ C2] ? console_lock_spinning_enable (kernel/printk/printk.c:1924) 
[ 621.590790][ C2] console_emit_next_record (kernel/printk/printk.c:3050 (discriminator 3) kernel/printk/printk.c:3137 (discriminator 3)) 
[ 621.590794][ C2] ? devkmsg_read (kernel/printk/printk.c:3082) 
[ 621.590798][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 621.590803][ C2] console_flush_all (kernel/printk/printk.c:3227) 
[ 621.590808][ C2] ? console_emit_next_record (kernel/printk/printk.c:3188) 
[ 621.590811][ C2] ? __lock_acquire (kernel/locking/lockdep.c:5237) 
[ 621.590816][ C2] console_unlock (kernel/printk/printk.c:3286 kernel/printk/printk.c:3325) 
[ 621.590819][ C2] ? console_flush_all (kernel/printk/printk.c:3320) 
[ 621.590822][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 621.590826][ C2] ? irq_work_single (kernel/irq_work.c:222) 
[ 621.590829][ C2] ? irq_work_single (kernel/irq_work.c:222) 
[ 621.590833][ C2] wake_up_klogd_work_func (kernel/printk/printk.c:4529) 
[ 621.590837][ C2] irq_work_single (kernel/irq_work.c:222) 
[ 621.590841][ C2] irq_work_run_list (kernel/irq_work.c:251 (discriminator 3)) 
[ 621.590844][ C2] ? irq_work_tick (kernel/irq_work.c:277) 
[ 621.590847][ C2] update_process_times (kernel/time/timer.c:2478) 
[ 621.590851][ C2] tick_nohz_handler (kernel/time/tick-sched.c:277 kernel/time/tick-sched.c:297) 
[ 621.590854][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 621.590858][ C2] __run_hrtimer (kernel/time/hrtimer.c:1761) 
[ 621.590861][ C2] ? tick_do_update_jiffies64.part.0 (kernel/time/tick-sched.c:285) 
[ 621.590866][ C2] __hrtimer_run_queues (./include/linux/timerqueue.h:25 kernel/time/hrtimer.c:1805) 
[ 621.590870][ C2] ? hrtimer_interrupt (kernel/time/hrtimer.c:640 (discriminator 2) kernel/time/hrtimer.c:1869 (discriminator 2)) 
[ 621.590874][ C2] ? __run_hrtimer (kernel/time/hrtimer.c:1795) 
[ 621.590877][ C2] ? kvm_clock_get_cycles (./arch/x86/include/asm/preempt.h:95 arch/x86/kernel/kvmclock.c:80 arch/x86/kernel/kvmclock.c:86) 
[ 621.590885][ C2] hrtimer_interrupt (kernel/time/hrtimer.c:1890) 
[ 621.590889][ C2] ? lockdep_softirqs_on (kernel/locking/lockdep.c:470 kernel/locking/lockdep.c:4558) 
[ 621.590894][ C2] __sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1057) 
[ 621.590898][ C2] sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1050 arch/x86/kernel/apic/apic.c:1050) 
[  621.590902][    C2]  </IRQ>
[  621.590903][    C2]  <TASK>
[ 621.590904][ C2] asm_sysvec_apic_timer_interrupt (./arch/x86/include/asm/idtentry.h:702) 
[ 621.590907][ C2] RIP: 0010:_raw_spin_unlock_irqrestore (./include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:194) 
[ 621.590911][ C2] Code: 74 24 10 e8 61 3b f9 fd 48 89 ef e8 89 8a f9 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> 4a c0 ed fd 65 8b 05 a3 fe 02 02 85 c0 74 0a 5b 5d c3 e8 e7 3d
All code
========
   0:	74 24                	je     0x26
   2:	10 e8                	adc    %ch,%al
   4:	61                   	(bad)
   5:	3b f9                	cmp    %ecx,%edi
   7:	fd                   	std
   8:	48 89 ef             	mov    %rbp,%rdi
   b:	e8 89 8a f9 fd       	call   0xfffffffffdf98a99
  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 4a c0 ed fd       	call   0xfffffffffdedc079		<-- trapping instruction
  2f:	65 8b 05 a3 fe 02 02 	mov    %gs:0x202fea3(%rip),%eax        # 0x202fed9
  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:	e7 3d                	out    %eax,$0x3d

Code starting with the faulting instruction
===========================================
   0:	e8 4a c0 ed fd       	call   0xfffffffffdedc04f
   5:	65 8b 05 a3 fe 02 02 	mov    %gs:0x202fea3(%rip),%eax        # 0x202feaf
   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:	e7 3d                	out    %eax,$0x3d
[  621.590914][    C2] RSP: 0018:ffffc900004a7a68 EFLAGS: 00000206
[  621.590918][    C2] RAX: 0000000000000002 RBX: 0000000000000200 RCX: 0000000000000080
[  621.590920][    C2] RDX: 0000000000000000 RSI: ffffffff8abeb534 RDI: 0000000000000001
[  621.590922][    C2] RBP: ffffffff8d46a7e0 R08: 0000000000000001 R09: 0000000000000001
[  621.590924][    C2] R10: ffffffff8ba1d317 R11: ffff8880060e8970 R12: ffffffff8d46a8e8
[  621.590927][    C2] R13: 00000000ffffffff R14: 0000000000000282 R15: ffffffff8d46a920
[ 621.590937][ 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) 
[ 621.590944][ C2] __receive_buf (drivers/tty/n_tty.c:1631) 
[ 621.590950][ C2] n_tty_receive_buf_common (drivers/tty/n_tty.c:1725) 
[ 621.590956][ C2] tty_port_default_receive_buf (drivers/tty/tty_port.c:39) 
[ 621.590962][ C2] flush_to_ldisc (drivers/tty/tty_buffer.c:445 drivers/tty/tty_buffer.c:495) 
[ 621.590970][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 621.590976][ C2] process_one_work (kernel/workqueue.c:3241) 
[ 621.590983][ C2] ? pwq_dec_nr_in_flight (kernel/workqueue.c:3138) 
[ 621.590988][ C2] ? assign_work (kernel/workqueue.c:1204) 
[ 621.590993][ C2] worker_thread (kernel/workqueue.c:3313 kernel/workqueue.c:3400) 
[ 621.590999][ C2] ? rescuer_thread (kernel/workqueue.c:3346) 
[ 621.591003][ C2] kthread (kernel/kthread.c:463) 
[ 621.591006][ C2] ? kthread_is_per_cpu (kernel/kthread.c:412) 
[ 621.591009][ C2] ? ret_from_fork (arch/x86/kernel/process.c:147) 
[ 621.591012][ C2] ? __lock_release (kernel/locking/lockdep.c:5536) 
[ 621.591015][ C2] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751) 
[ 621.591019][ C2] ? kthread_is_per_cpu (kernel/kthread.c:412) 
[ 621.591022][ C2] ret_from_fork (arch/x86/kernel/process.c:154) 
[ 621.591025][ 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