======================================
| [ 4093.643916][   T11]
| [ 4093.648247][   T11] ------------[ cut here ]------------
| [ 4093.648611][ T11] WARNING: CPU: 1 PID: 11 at lib/ref_tracker.c:179 ref_tracker_dir_exit (lib/ref_tracker.c:179) 
| [ 4093.649141][   T11] Modules linked in: drop_monitor netdevsim cls_matchall bonding psample macsec ip6_gre ip_gre gre cls_u32 sch_htb act_gact cls_flower sch_ingress sha1_generic xfrm_user xt_policy nft_compat nf_tables libcrc32c vxlan mpls_iptunnel mpls_router [last unloaded: netdevsim]
[ 4093.651151][   T11] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 4093.651818][   T11] Workqueue: netns cleanup_net
[ 4093.652072][ T11] RIP: 0010:ref_tracker_dir_exit (lib/ref_tracker.c:179) 
[ 4093.652423][ T11] Code: 38 00 0f 85 58 02 00 00 49 8b 04 24 4d 89 e6 4c 39 e5 0f 85 2a ff ff ff 48 8b 1c 24 48 8b 74 24 10 48 89 df e8 b9 74 ab 01 90 <0f> 0b 90 48 8d 6b 4c be 04 00 00 00 48 89 ef e8 84 07 95 ff 48 89
All code
========
   0:	38 00                	cmp    %al,(%rax)
   2:	0f 85 58 02 00 00    	jne    0x260
   8:	49 8b 04 24          	mov    (%r12),%rax
   c:	4d 89 e6             	mov    %r12,%r14
   f:	4c 39 e5             	cmp    %r12,%rbp
  12:	0f 85 2a ff ff ff    	jne    0xffffffffffffff42
  18:	48 8b 1c 24          	mov    (%rsp),%rbx
  1c:	48 8b 74 24 10       	mov    0x10(%rsp),%rsi
  21:	48 89 df             	mov    %rbx,%rdi
  24:	e8 b9 74 ab 01       	call   0x1ab74e2
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	48 8d 6b 4c          	lea    0x4c(%rbx),%rbp
  31:	be 04 00 00 00       	mov    $0x4,%esi
  36:	48 89 ef             	mov    %rbp,%rdi
  39:	e8 84 07 95 ff       	call   0xffffffffff9507c2
  3e:	48                   	rex.W
  3f:	89                   	.byte 0x89

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	48 8d 6b 4c          	lea    0x4c(%rbx),%rbp
   7:	be 04 00 00 00       	mov    $0x4,%esi
   c:	48 89 ef             	mov    %rbp,%rdi
   f:	e8 84 07 95 ff       	call   0xffffffffff950798
  14:	48                   	rex.W
  15:	89                   	.byte 0x89
DETECTED CRASH, lowering timeout

[ 4093.653499][   T11] RSP: 0018:ffffc900000bfb70 EFLAGS: 00010286
[ 4093.653847][   T11] RAX: 0000000000000006 RBX: ffff88800f1d0238 RCX: 1ffffffff47f375d
[ 4093.654274][   T11] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffa0ab2b41
[ 4093.654734][   T11] RBP: ffff88800f1d0290 R08: 0000000000000001 R09: fffffbfff47ebc86
[ 4093.655160][   T11] R10: ffffffffa3f5e437 R11: ffffc900000bf7b1 R12: ffff88800f1d0290
[ 4093.655586][   T11] R13: dead000000000100 R14: ffff88800f1d0290 R15: dffffc0000000000
[ 4093.656047][   T11] FS:  0000000000000000(0000) GS:ffff888035600000(0000) knlGS:0000000000000000
[ 4093.656535][   T11] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 4093.656900][   T11] CR2: 0000558dd5c13dec CR3: 000000002dd36006 CR4: 0000000000770ef0
[ 4093.657350][   T11] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 4093.657780][   T11] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 4093.658188][   T11] PKRU: 55555554
[ 4093.658386][   T11] Call Trace:
[ 4093.658563][   T11]  <TASK>
[ 4093.658721][ T11] ? __warn (kernel/panic.c:677) 
[ 4093.658943][ T11] ? ref_tracker_dir_exit (lib/ref_tracker.c:179) 
[ 4093.659236][ T11] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 4093.659484][ T11] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 4093.659716][ T11] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 4093.659964][ T11] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 4093.660249][ T11] ? _raw_spin_unlock_irqrestore (./include/linux/spinlock_api_smp.h:151 kernel/locking/spinlock.c:194) 
[ 4093.660554][ T11] ? ref_tracker_dir_exit (lib/ref_tracker.c:179) 
[ 4093.660842][ T11] ? __pfx_ref_tracker_dir_exit (lib/ref_tracker.c:158) 
[ 4093.661145][ T11] ? kfree (mm/slub.c:4299 mm/slub.c:4409) 
[ 4093.661373][ T11] cleanup_net (net/core/net_namespace.c:464 net/core/net_namespace.c:456 net/core/net_namespace.c:658) 
[ 4093.661611][ T11] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5719) 
[ 4093.661905][ T11] ? __pfx_cleanup_net (net/core/net_namespace.c:581) 
[ 4093.662206][ T11] ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5725) 
[ 4093.662462][ T11] ? process_one_work (kernel/workqueue.c:2609) 
[ 4093.662767][ T11] process_one_work (kernel/workqueue.c:2633) 
[ 4093.663068][ T11] ? hlock_class (./arch/x86/include/asm/bitops.h:227 ./arch/x86/include/asm/bitops.h:239 ./include/asm-generic/bitops/instrumented-non-atomic.h:142 kernel/locking/lockdep.c:228) 
[ 4093.663320][ T11] ? __pfx_process_one_work (kernel/workqueue.c:2542) 
[ 4093.663622][ T11] ? assign_work (kernel/workqueue.c:1101) 
[ 4093.663877][ T11] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 4093.664158][ T11] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 4093.664464][ T11] kthread (kernel/kthread.c:388) 
[ 4093.664705][ T11] ? __pfx_kthread (kernel/kthread.c:341) 
[ 4093.664959][ T11] ret_from_fork (arch/x86/kernel/process.c:147) 
[ 4093.665234][ T11] ? __pfx_kthread (kernel/kthread.c:341) 


Finger prints:
ref_tracker_dir_exit:cleanup_net:process_one_work:worker_thread