======================================
| [  153.363621] ------------[ cut here ]------------
| [  153.363680] refcount_t: underflow; use-after-free.
| [  153.363755] WARNING: CPU: 1 PID: 266 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [  153.363835] Modules linked in: cls_matchall
[  153.363944] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  153.363988] Workqueue: netns cleanup_net
[  153.364024] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[  153.364062] Code: b0 e8 88 98 ba ff 90 0f 0b 90 90 c3 80 3d 69 b4 eb 00 00 75 89 c6 05 60 b4 eb 00 01 90 48 c7 c7 98 6e b4 b0 e8 65 98 ba ff 90 <0f> 0b 90 90 c3 80 3d 44 b4 eb 00 00 0f 85 62 ff ff ff c6 05 37 b4
All code
========
   0:	b0 e8                	mov    $0xe8,%al
   2:	88 98 ba ff 90 0f    	mov    %bl,0xf90ffba(%rax)
   8:	0b 90 90 c3 80 3d    	or     0x3d80c390(%rax),%edx
   e:	69 b4 eb 00 00 75 89 	imul   $0xb46005c6,-0x768b0000(%rbx,%rbp,8),%esi
  15:	c6 05 60 b4 
  19:	eb 00                	jmp    0x1b
  1b:	01 90 48 c7 c7 98    	add    %edx,-0x673838b8(%rax)
  21:	6e                   	outsb  %ds:(%rsi),(%dx)
  22:	b4 b0                	mov    $0xb0,%ah
  24:	e8 65 98 ba ff       	call   0xffffffffffba988e
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	c3                   	ret
  2f:	80 3d 44 b4 eb 00 00 	cmpb   $0x0,0xebb444(%rip)        # 0xebb47a
  36:	0f 85 62 ff ff ff    	jne    0xffffffffffffff9e
  3c:	c6                   	.byte 0xc6
  3d:	05                   	.byte 0x5
  3e:	37                   	(bad)
  3f:	b4                   	.byte 0xb4

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	90                   	nop
   4:	c3                   	ret
   5:	80 3d 44 b4 eb 00 00 	cmpb   $0x0,0xebb444(%rip)        # 0xebb450
   c:	0f 85 62 ff ff ff    	jne    0xffffffffffffff74
  12:	c6                   	.byte 0xc6
  13:	05                   	.byte 0x5
  14:	37                   	(bad)
  15:	b4                   	.byte 0xb4
[  153.364205] RSP: 0018:ffffb496c02b3d50 EFLAGS: 00010286
[  153.364247] RAX: 0000000000000000 RBX: ffffb496c02b3d60 RCX: 00000000ffffdfff
[  153.364301] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  153.364358] RBP: ffffb496c02b3878 R08: ffffffffb0f56a28 R09: 00000000ffffdfff
[  153.364414] R10: ffffffffb0e76a40 R11: ffffffffb0f26a40 R12: dead000000000122
[  153.364474] R13: 00000000fffdc2b5 R14: 0000000000000001 R15: ffff93fbc45dd000
[  153.364533] FS:  0000000000000000(0000) GS:ffff93fc4d637000(0000) knlGS:0000000000000000
[  153.364599] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  153.364652] CR2: 00007f244db39730 CR3: 0000000039c41004 CR4: 0000000000772ef0
[  153.364715] PKRU: 55555554
[  153.364733] Call Trace:
[  153.364762]  <TASK>
[  153.364787]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[  153.364832]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[  153.364870]  cleanup_net (net/core/net_namespace.c:698)
[  153.364908]  process_one_work (kernel/workqueue.c:3268)
[  153.364947]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  153.364986]  ? rescuer_thread (kernel/workqueue.c:3373)
[  153.365018]  kthread (kernel/kthread.c:463)
[  153.365064]  ? kthreads_online_cpu (kernel/kthread.c:412)
[  153.365116]  ? kthreads_online_cpu (kernel/kthread.c:412)
[  153.365155]  ret_from_fork (arch/x86/kernel/process.c:164)
[  153.365192]  ? kthreads_online_cpu (kernel/kthread.c:412)


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