======================================
| xx__-> [    3.782501] ------------[ cut here ]------------
| [    3.782570] refcount_t: underflow; use-after-free.
| [    3.782627] WARNING: CPU: 3 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [    3.782695] Modules linked in: nft_ct nf_conntrack_netlink veth nft_nat nft_numgen nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables
[    3.782913] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    3.782960] Workqueue: netns cleanup_net
[    3.782993] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[    3.783033] Code: 86 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 d1 86 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:	86 e8                	xchg   %ch,%al
   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 d1 86 	mov    $0xffffffff86d1de78,%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)
[    3.783155] RSP: 0018:ffff9839c025fd50 EFLAGS: 00010286
[    3.783204] RAX: 0000000000000000 RBX: ffff9839c025fd60 RCX: 00000000ffffdfff
[    3.783260] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[    3.783315] RBP: ffff9839c025f868 R08: ffffffff87156d28 R09: 00000000ffffdfff
[    3.783371] R10: ffffffff87076d40 R11: ffffffff87126d40 R12: dead000000000122
[    3.783421] R13: 00000000fffb7a64 R14: 0000000000000001 R15: ffff8d2205224000
[    3.783476] FS:  0000000000000000(0000) GS:ffff8d22b7558000(0000) knlGS:0000000000000000
[    3.783535] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    3.783583] CR2: 00007f358fcdc760 CR3: 0000000024841002 CR4: 0000000000772ef0
[    3.783641] PKRU: 55555554
[    3.783663] Call Trace:
[    3.783688]  <TASK>
[    3.783710]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[    3.783744]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[    3.783787]  cleanup_net (net/core/net_namespace.c:698)
[    3.783818]  process_one_work (kernel/workqueue.c:3268)
[    3.783862]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[    3.783903]  ? rescuer_thread (kernel/workqueue.c:3373)
[    3.783935]  kthread (kernel/kthread.c:463)
[    3.783968]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    3.784007]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    3.784047]  ret_from_fork (arch/x86/kernel/process.c:164)
[    3.784084]  ? kthreads_online_cpu (kernel/kthread.c:412)


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