======================================
| xx__-> [    6.937269] ------------[ cut here ]------------
| [    6.937356] refcount_t: underflow; use-after-free.
| [    6.937428] WARNING: CPU: 0 PID: 67 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [    6.937531] Modules linked in: nf_conntrack_netlink nft_masq nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables
[    6.937750] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    6.937811] Workqueue: netns cleanup_net
[    6.937850] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[    6.937897] Code: 9b 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 31 9b 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:	9b                   	fwait
   1:	e8 18 ed b9 ff       	call   0xffffffffffb9ed1e
   6:	90                   	nop
   7:	0f 0b                	ud2
   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 31 9b 	mov    $0xffffffff9b31de78,%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)
[    6.938076] RSP: 0018:ffffb15a40257d50 EFLAGS: 00010286
[    6.938123] RAX: 0000000000000000 RBX: ffffb15a40257d60 RCX: 00000000ffffdfff
[    6.938191] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[    6.938269] RBP: ffffb15a40257868 R08: ffffffff9b756d28 R09: 00000000ffffdfff
[    6.938335] R10: ffffffff9b676d40 R11: ffffffff9b726d40 R12: dead000000000122
[    6.938396] R13: 00000000fffb86a5 R14: 0000000000000001 R15: ffff98fa83821000
[    6.938465] FS:  0000000000000000(0000) GS:ffff98fb22dd8000(0000) knlGS:0000000000000000
[    6.938532] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    6.938604] CR2: 000055b75e662dec CR3: 000000000398c006 CR4: 0000000000772ef0
[    6.938689] PKRU: 55555554
[    6.938718] Call Trace:
[    6.938752]  <TASK>
[    6.938776]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[    6.938820]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[    6.938864]  cleanup_net (net/core/net_namespace.c:698)
[    6.938900]  process_one_work (kernel/workqueue.c:3268)
[    6.938947]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[    6.938992]  ? rescuer_thread (kernel/workqueue.c:3373)
[    6.939035]  kthread (kernel/kthread.c:463)
[    6.939098]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    6.939145]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    6.939193]  ret_from_fork (arch/x86/kernel/process.c:164)
[    6.939249]  ? kthreads_online_cpu (kernel/kthread.c:412)


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