======================================
| [    2.029508] ------------[ cut here ]------------
| [    2.029600] refcount_t: underflow; use-after-free.
| [    2.029663] WARNING: CPU: 1 PID: 66 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [    2.029738] Modules linked in:
[    2.029843] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    2.029896] Workqueue: netns cleanup_net
[    2.029936] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[    2.029981] Code: 98 e8 e8 54 ba ff 90 0f 0b 90 90 c3 80 3d 00 e6 2b 01 00 75 89 c6 05 f7 e5 2b 01 01 90 48 c7 c7 f8 48 55 98 e8 c5 54 ba ff 90 <0f> 0b 90 90 c3 80 3d db e5 2b 01 00 0f 85 62 ff ff ff c6 05 ce e5
All code
========
   0:	98                   	cwtl
   1:	e8 e8 54 ba ff       	call   0xffffffffffba54ee
   6:	90                   	nop
   7:	0f 0b                	ud2
   9:	90                   	nop
   a:	90                   	nop
   b:	c3                   	ret
   c:	80 3d 00 e6 2b 01 00 	cmpb   $0x0,0x12be600(%rip)        # 0x12be613
  13:	75 89                	jne    0xffffffffffffff9e
  15:	c6 05 f7 e5 2b 01 01 	movb   $0x1,0x12be5f7(%rip)        # 0x12be613
  1c:	90                   	nop
  1d:	48 c7 c7 f8 48 55 98 	mov    $0xffffffff985548f8,%rdi
  24:	e8 c5 54 ba ff       	call   0xffffffffffba54ee
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	c3                   	ret
  2f:	80 3d db e5 2b 01 00 	cmpb   $0x0,0x12be5db(%rip)        # 0x12be611
  36:	0f 85 62 ff ff ff    	jne    0xffffffffffffff9e
  3c:	c6                   	.byte 0xc6
  3d:	05                   	.byte 0x5
  3e:	ce                   	(bad)
  3f:	e5                   	.byte 0xe5

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	90                   	nop
   4:	c3                   	ret
   5:	80 3d db e5 2b 01 00 	cmpb   $0x0,0x12be5db(%rip)        # 0x12be5e7
   c:	0f 85 62 ff ff ff    	jne    0xffffffffffffff74
  12:	c6                   	.byte 0xc6
  13:	05                   	.byte 0x5
  14:	ce                   	(bad)
  15:	e5                   	.byte 0xe5
[    2.030115] RSP: 0018:ffffb10ec024fd50 EFLAGS: 00010286
[    2.030157] RAX: 0000000000000000 RBX: ffffb10ec024fd60 RCX: 00000000ffffdfff
[    2.030218] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[    2.030272] RBP: ffffb10ec024f858 R08: ffffffff98d5ba28 R09: 00000000ffffdfff
[    2.030333] R10: ffffffff98c7ba40 R11: ffffffff98d2ba40 R12: dead000000000122
[    2.030394] R13: 00000000fffb7387 R14: 0000000000000001 R15: ffff88b404f7f000
[    2.030457] FS:  0000000000000000(0000) GS:ffff88b4a5811000(0000) knlGS:0000000000000000
[    2.030521] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    2.030573] CR2: 00007fca309ad730 CR3: 000000003a846003 CR4: 0000000000772ef0
[    2.030636] PKRU: 55555554
[    2.030659] Call Trace:
[    2.030685]  <TASK>
[    2.030708]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[    2.030742]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[    2.030777]  cleanup_net (net/core/net_namespace.c:698)
[    2.030810]  process_one_work (kernel/workqueue.c:3268)
[    2.030850]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[    2.030886]  ? rescuer_thread (kernel/workqueue.c:3373)
[    2.030920]  kthread (kernel/kthread.c:463)
[    2.030954]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    2.030998]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    2.031042]  ret_from_fork (arch/x86/kernel/process.c:164)
[    2.031082]  ? kthreads_online_cpu (kernel/kthread.c:412)


Finger prints:
refcount_warn_saturate:netdev_run_todo:ops_undo_list:cleanup_net:process_one_work