======================================
| [    2.963049] ------------[ cut here ]------------
| [    2.963141] refcount_t: underflow; use-after-free.
| [    2.963210] WARNING: CPU: 3 PID: 66 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [    2.963302] Modules linked in: sch_fq
[    2.963447] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    2.963513] Workqueue: netns cleanup_net
[    2.963561] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[    2.963614] Code: 84 e8 e8 54 ba ff 90 0f 0b 90 90 c3 80 3d 00 e6 2b 01 00 75 89 c6 05 f7 e5 2b 01 01 90 48 c7 c7 f8 48 d5 84 e8 c5 54 ba ff 90 <0f> 0b 90 90 c3 80 3d db e5 2b 01 00 0f 85 62 ff ff ff c6 05 ce e5
All code
========
   0:	84 e8                	test   %ch,%al
   2:	e8 54 ba ff 90       	call   0xffffffff90ffba5b
   7:	0f 0b                	ud2
   9:	90                   	nop
   a:	90                   	nop
   b:	c3                   	ret
   c:	80 3d 00 e6 2b 01 00 	cmpb   $0x0,0x12be600(%rip)        # 0x12be613
  13:	75 89                	jne    0xffffffffffffff9e
  15:	c6 05 f7 e5 2b 01 01 	movb   $0x1,0x12be5f7(%rip)        # 0x12be613
  1c:	90                   	nop
  1d:	48 c7 c7 f8 48 d5 84 	mov    $0xffffffff84d548f8,%rdi
  24:	e8 c5 54 ba ff       	call   0xffffffffffba54ee
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	c3                   	ret
  2f:	80 3d db e5 2b 01 00 	cmpb   $0x0,0x12be5db(%rip)        # 0x12be611
  36:	0f 85 62 ff ff ff    	jne    0xffffffffffffff9e
  3c:	c6                   	.byte 0xc6
  3d:	05                   	.byte 0x5
  3e:	ce                   	(bad)
  3f:	e5                   	.byte 0xe5

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	90                   	nop
   4:	c3                   	ret
   5:	80 3d db e5 2b 01 00 	cmpb   $0x0,0x12be5db(%rip)        # 0x12be5e7
   c:	0f 85 62 ff ff ff    	jne    0xffffffffffffff74
  12:	c6                   	.byte 0xc6
  13:	05                   	.byte 0x5
  14:	ce                   	(bad)
  15:	e5                   	.byte 0xe5
[    2.963798] RSP: 0018:ffff9a7d0024fd50 EFLAGS: 00010286
[    2.963860] RAX: 0000000000000000 RBX: ffff9a7d0024fd60 RCX: 00000000ffffdfff
[    2.963938] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[    2.964025] RBP: ffff9a7d0024f858 R08: ffffffff8555ba28 R09: 00000000ffffdfff
[    2.964104] R10: ffffffff8547ba40 R11: ffffffff8552ba40 R12: dead000000000122
[    2.964184] R13: 00000000fffb772c R14: 0000000000000001 R15: ffff8d2fc5dc2000
[    2.964265] FS:  0000000000000000(0000) GS:ffff8d3079111000(0000) knlGS:0000000000000000
[    2.964353] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    2.964417] CR2: 00007fb7df4be4d8 CR3: 0000000012e46001 CR4: 0000000000772ef0
[    2.964498] PKRU: 55555554
[    2.964523] Call Trace:
[    2.964551]  <TASK>
[    2.964576]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[    2.964617]  ops_undo_list (net/core/net_namespace.c:190 net/core/net_namespace.c:248)
[    2.964655]  cleanup_net (net/core/net_namespace.c:698)
[    2.964696]  process_one_work (kernel/workqueue.c:3268)
[    2.964746]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[    2.964785]  ? rescuer_thread (kernel/workqueue.c:3373)
[    2.964826]  kthread (kernel/kthread.c:463)
[    2.964867]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    2.964922]  ? kthreads_online_cpu (kernel/kthread.c:412)
[    2.964978]  ret_from_fork (arch/x86/kernel/process.c:164)
[    2.965025]  ? kthreads_online_cpu (kernel/kthread.c:412)


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