======================================
| [    4.932235] ------------[ cut here ]------------
| [    4.932325] refcount_t: underflow; use-after-free.
| [    4.932409] WARNING: CPU: 0 PID: 67 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [    4.932519] Modules linked in: sctp ip6_udp_tunnel udp_tunnel xt_conntrack nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nft_compat nf_tables x_tables sch_netem cls_u32 sch_htb veth
[    4.932761] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    4.932822] Workqueue: netns cleanup_net
[    4.932862] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[    4.932911] Code: 8a e8 18 ed b9 ff 90 0f 0b 90 90 c3 80 3d d9 ea ea 00 00 75 89 c6 05 d0 ea ea 00 01 90 48 c7 c7 78 de f1 8a e8 f5 ec b9 ff 90 <0f> 0b 90 90 c3 80 3d b4 ea ea 00 00 0f 85 62 ff ff ff c6 05 a7 ea
All code
========
   0:	8a e8                	mov    %al,%ch
   2:	18 ed                	sbb    %ch,%ch
   4:	b9 ff 90 0f 0b       	mov    $0xb0f90ff,%ecx
   9:	90                   	nop
   a:	90                   	nop
   b:	c3                   	ret
   c:	80 3d d9 ea ea 00 00 	cmpb   $0x0,0xeaead9(%rip)        # 0xeaeaec
  13:	75 89                	jne    0xffffffffffffff9e
  15:	c6 05 d0 ea ea 00 01 	movb   $0x1,0xeaead0(%rip)        # 0xeaeaec
  1c:	90                   	nop
  1d:	48 c7 c7 78 de f1 8a 	mov    $0xffffffff8af1de78,%rdi
  24:	e8 f5 ec b9 ff       	call   0xffffffffffb9ed1e
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	c3                   	ret
  2f:	80 3d b4 ea ea 00 00 	cmpb   $0x0,0xeaeab4(%rip)        # 0xeaeaea
  36:	0f 85 62 ff ff ff    	jne    0xffffffffffffff9e
  3c:	c6                   	.byte 0xc6
  3d:	05                   	.byte 0x5
  3e:	a7                   	cmpsl  %es:(%rdi),%ds:(%rsi)
  3f:	ea                   	(bad)

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	90                   	nop
   4:	c3                   	ret
   5:	80 3d b4 ea ea 00 00 	cmpb   $0x0,0xeaeab4(%rip)        # 0xeaeac0
   c:	0f 85 62 ff ff ff    	jne    0xffffffffffffff74
  12:	c6                   	.byte 0xc6
  13:	05                   	.byte 0x5
  14:	a7                   	cmpsl  %es:(%rdi),%ds:(%rsi)
  15:	ea                   	(bad)
[    4.933071] RSP: 0000:ffffa4a300257d50 EFLAGS: 00010286
[    4.933119] RAX: 0000000000000000 RBX: ffffa4a300257d60 RCX: 00000000ffffdfff
[    4.933194] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[    4.933257] RBP: ffffa4a300257868 R08: ffffffff8b356d28 R09: 00000000ffffdfff
[    4.933315] R10: ffffffff8b276d40 R11: ffffffff8b326d40 R12: dead000000000122
[    4.933377] R13: 00000000fffb7ee4 R14: 0000000000000001 R15: ffff911dc1f67000
[    4.933437] FS:  0000000000000000(0000) GS:ffff911e731d8000(0000) knlGS:0000000000000000
[    4.933516] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    4.933580] CR2: 00007f35e93c6ae4 CR3: 0000000006618006 CR4: 0000000000772ef0
[    4.933644] PKRU: 55555554
[    4.933670] Call Trace:
[    4.933689]  <TASK>
[    4.933709]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[    4.933754]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[    4.933794]  cleanup_net (net/core/net_namespace.c:698)
[    4.933835]  process_one_work (kernel/workqueue.c:3268)
[    4.933876]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[    4.933911]  ? rescuer_thread (kernel/workqueue.c:3373)
[    4.933949]  kthread (kernel/kthread.c:463)
[    4.933998]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    4.934043]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    4.934100]  ret_from_fork (arch/x86/kernel/process.c:164)
[    4.934139]  ? kthreads_online_cpu (kernel/kthread.c:412)


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