======================================
| [  104.826015] ------------[ cut here ]------------
| [  104.826148] refcount_t: underflow; use-after-free.
| [  104.826269] WARNING: CPU: 3 PID: 65 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [  104.826382] Modules linked in: sch_netem
[  104.826523] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  104.826593] Workqueue: netns cleanup_net
[  104.826701] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[  104.826762] Code: b0 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 b0 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:	b0 e8                	mov    $0xe8,%al
   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 b0 	mov    $0xffffffffb0f24ac8,%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
[  104.826951] RSP: 0018:ffffc1b5c0247d50 EFLAGS: 00010286
[  104.827010] RAX: 0000000000000000 RBX: ffffc1b5c0247d60 RCX: 00000000ffffdfff
[  104.827087] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  104.827170] RBP: ffffc1b5c0247878 R08: ffffffffb135ca28 R09: 00000000ffffdfff
[  104.827245] R10: ffffffffb127ca40 R11: ffffffffb132ca40 R12: dead000000000122
[  104.827321] R13: 00000000fffd0512 R14: 0000000000000001 R15: ffff9c4183218000
[  104.827404] FS:  0000000000000000(0000) GS:ffff9c420d340000(0000) knlGS:0000000000000000
[  104.827487] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  104.827554] CR2: 000055ceb3bd2dec CR3: 0000000002f66003 CR4: 0000000000772ef0
[  104.827656] PKRU: 55555554
[  104.827695] Call Trace:
[  104.827728]  <TASK>
[  104.827761]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[  104.827821]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[  104.827873]  cleanup_net (net/core/net_namespace.c:698)
[  104.827920]  process_one_work (kernel/workqueue.c:3268)
[  104.827983]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  104.828026]  ? rescuer_thread (kernel/workqueue.c:3373)
[  104.828072]  kthread (kernel/kthread.c:463)
[  104.828128]  ? kthreads_online_cpu (kernel/kthread.c:412)
[  104.828185]  ? kthreads_online_cpu (kernel/kthread.c:412)
[  104.828236]  ret_from_fork (arch/x86/kernel/process.c:164)
[  104.828295]  ? kthreads_online_cpu (kernel/kthread.c:412)


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