======================================
| [  153.690798] ------------[ cut here ]------------
| [  153.690877] refcount_t: underflow; use-after-free.
| [  153.690949] WARNING: CPU: 3 PID: 3725 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [  153.691060] Modules linked in: cls_matchall
[  153.691163] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  153.691218] Workqueue: netns cleanup_net
[  153.691248] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[  153.691304] Code: 89 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 74 89 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:	89 e8                	mov    %ebp,%eax
   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:	74 89                	je     0xffffffffffffffad
  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
[  153.691461] RSP: 0000:ffffb74c81e1bd50 EFLAGS: 00010286
[  153.691500] RAX: 0000000000000000 RBX: ffffb74c81e1bd60 RCX: 00000000ffffdfff
[  153.691546] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  153.691598] RBP: ffffb74c81e1b878 R08: ffffffff89b56a28 R09: 00000000ffffdfff
[  153.691644] R10: ffffffff89a76a40 R11: ffffffff89b26a40 R12: dead000000000122
[  153.691699] R13: 00000000fffdc3fa R14: 0000000000000001 R15: ffff94c805caa000
[  153.691801] FS:  0000000000000000(0000) GS:ffff94c8b4b37000(0000) knlGS:0000000000000000
[  153.691859] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  153.691906] CR2: 00007fcc2cb7c9c0 CR3: 0000000005c51004 CR4: 0000000000772ef0
[  153.691954] PKRU: 55555554
[  153.691979] Call Trace:
[  153.691996]  <TASK>
[  153.692021]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[  153.692057]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[  153.692088]  cleanup_net (net/core/net_namespace.c:698)
[  153.692119]  process_one_work (kernel/workqueue.c:3268)
[  153.692150]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  153.692182]  ? rescuer_thread (kernel/workqueue.c:3373)
[  153.692214]  kthread (kernel/kthread.c:463)
[  153.692245]  ? kthreads_online_cpu (kernel/kthread.c:412)
[  153.692284]  ? kthreads_online_cpu (kernel/kthread.c:412)
[  153.692323]  ret_from_fork (arch/x86/kernel/process.c:164)
[  153.692356]  ? kthreads_online_cpu (kernel/kthread.c:412)


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