======================================
| xx__-> [   13.942393] ------------[ cut here ]------------
| [   13.942463] refcount_t: underflow; use-after-free.
| [   13.942528] WARNING: CPU: 3 PID: 67 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [   13.942596] Modules linked in:
[   13.942724] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   13.942793] Workqueue: netns cleanup_net
[   13.942843] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[   13.942899] Code: b4 e8 48 df ba ff 90 0f 0b 90 90 c3 80 3d c9 50 ec 00 00 75 89 c6 05 c0 50 ec 00 01 90 48 c7 c7 c8 4a f2 b4 e8 25 df ba ff 90 <0f> 0b 90 90 c3 80 3d a4 50 ec 00 00 0f 85 62 ff ff ff c6 05 97 50
All code
========
   0:	b4 e8                	mov    $0xe8,%ah
   2:	48 df ba ff 90 0f 0b 	rex.W fistpll 0xb0f90ff(%rdx)
   9:	90                   	nop
   a:	90                   	nop
   b:	c3                   	ret
   c:	80 3d c9 50 ec 00 00 	cmpb   $0x0,0xec50c9(%rip)        # 0xec50dc
  13:	75 89                	jne    0xffffffffffffff9e
  15:	c6 05 c0 50 ec 00 01 	movb   $0x1,0xec50c0(%rip)        # 0xec50dc
  1c:	90                   	nop
  1d:	48 c7 c7 c8 4a f2 b4 	mov    $0xffffffffb4f24ac8,%rdi
  24:	e8 25 df ba ff       	call   0xffffffffffbadf4e
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	c3                   	ret
  2f:	80 3d a4 50 ec 00 00 	cmpb   $0x0,0xec50a4(%rip)        # 0xec50da
  36:	0f 85 62 ff ff ff    	jne    0xffffffffffffff9e
  3c:	c6                   	.byte 0xc6
  3d:	05                   	.byte 0x5
  3e:	97                   	xchg   %eax,%edi
  3f:	50                   	push   %rax

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	90                   	nop
   4:	c3                   	ret
   5:	80 3d a4 50 ec 00 00 	cmpb   $0x0,0xec50a4(%rip)        # 0xec50b0
   c:	0f 85 62 ff ff ff    	jne    0xffffffffffffff74
  12:	c6                   	.byte 0xc6
  13:	05                   	.byte 0x5
  14:	97                   	xchg   %eax,%edi
  15:	50                   	push   %rax
[   13.943035] RSP: 0018:ffffb80840257d50 EFLAGS: 00010286
[   13.943077] RAX: 0000000000000000 RBX: ffffb80840257d60 RCX: 00000000ffffdfff
[   13.943159] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   13.943227] RBP: ffffb80840257878 R08: ffffffffb535ca28 R09: 00000000ffffdfff
[   13.943277] R10: ffffffffb527ca40 R11: ffffffffb532ca40 R12: dead000000000122
[   13.943332] R13: 00000000fffba213 R14: 0000000000000001 R15: ffff9094c4ab4000
[   13.943391] FS:  0000000000000000(0000) GS:ffff909549340000(0000) knlGS:0000000000000000
[   13.943458] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   13.943534] CR2: 0000563bacfa1dec CR3: 000000000a79c002 CR4: 0000000000772ef0
[   13.943598] PKRU: 55555554
[   13.943619] Call Trace:
[   13.943638]  <TASK>
[   13.943658]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[   13.943699]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[   13.943746]  cleanup_net (net/core/net_namespace.c:698)
[   13.943790]  process_one_work (kernel/workqueue.c:3268)
[   13.943828]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   13.943862]  ? rescuer_thread (kernel/workqueue.c:3373)
[   13.943891]  kthread (kernel/kthread.c:463)
[   13.943922]  ? kthreads_online_cpu (kernel/kthread.c:412)
[   13.943978]  ? kthreads_online_cpu (kernel/kthread.c:412)
[   13.944028]  ret_from_fork (arch/x86/kernel/process.c:164)
[   13.944071]  ? kthreads_online_cpu (kernel/kthread.c:412)


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