======================================
| [  104.098794] ------------[ cut here ]------------
| [  104.099032] refcount_t: underflow; use-after-free.
| [  104.099121] WARNING: CPU: 2 PID: 66 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [  104.099236] Modules linked in: sch_netem
[  104.099422] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  104.099524] Workqueue: netns cleanup_net
[  104.099591] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[  104.099666] Code: ac 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 92 ac 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:	ac                   	lods   %ds:(%rsi),%al
   1:	e8 48 df ba ff       	call   0xffffffffffbadf4e
   6:	90                   	nop
   7:	0f 0b                	ud2
   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 92 ac 	mov    $0xffffffffac924ac8,%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
[  104.099877] RSP: 0018:ffffb5824024fd50 EFLAGS: 00010286
[  104.099952] RAX: 0000000000000000 RBX: ffffb5824024fd60 RCX: 00000000ffffdfff
[  104.100053] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  104.100150] RBP: ffffb5824024f878 R08: ffffffffacd5ca28 R09: 00000000ffffdfff
[  104.100255] R10: ffffffffacc7ca40 R11: ffffffffacd2ca40 R12: dead000000000122
[  104.100355] R13: 00000000fffd0241 R14: 0000000000000001 R15: ffff8a610112c000
[  104.100456] FS:  0000000000000000(0000) GS:ffff8a61918c0000(0000) knlGS:0000000000000000
[  104.100558] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  104.100644] CR2: 00000000004061e9 CR3: 0000000001b24002 CR4: 0000000000772ef0
[  104.100751] PKRU: 55555554
[  104.100801] Call Trace:
[  104.100856]  <TASK>
[  104.100912]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[  104.100984]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[  104.101050]  cleanup_net (net/core/net_namespace.c:698)
[  104.101111]  process_one_work (kernel/workqueue.c:3268)
[  104.101181]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  104.101252]  ? rescuer_thread (kernel/workqueue.c:3373)
[  104.101317]  kthread (kernel/kthread.c:463)
[  104.101385]  ? kthreads_online_cpu (kernel/kthread.c:412)
[  104.101459]  ? kthreads_online_cpu (kernel/kthread.c:412)
[  104.101532]  ret_from_fork (arch/x86/kernel/process.c:164)
[  104.101598]  ? kthreads_online_cpu (kernel/kthread.c:412)


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