======================================
| xx__-> [ 2006.759398][   T12] ------------[ cut here ]------------
| [ 2006.759733][   T12] conntrack cleanup blocked for 60s
| [ 2006.759735][   T12] WARNING: net/netfilter/nf_conntrack_core.c:2511 at 0x0, CPU#3: kworker/u16:0/12
| [ 2006.760106][   T12] Modules linked in: xt_conntrack nf_conntrack nf_defrag_ipv4 nf_defrag_ipv6 geneve ip6_gre ip_gre gre cls_matchall xfrm_user xt_policy nft_compat nf_tables act_gact cls_flower sch_ingress vxlan
[ 2006.761164][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 2006.761319][   T12] Workqueue: netns cleanup_net
[ 2006.761536][   T12] RIP: 0010:nf_conntrack_cleanup_net_list (net/netfilter/nf_conntrack_core.c:2511 (discriminator 16)) nf_conntrack
[ 2006.761736][   T12] Code: 00 48 8b 54 24 18 48 8b 05 c3 88 a6 ec 48 81 c2 60 ea 00 00 48 39 c2 78 0a e8 42 0e 96 eb e9 25 fd ff ff 48 8d 3d 56 56 d7 ff <67> 48 0f b9 3a eb e8 48 8b 5c 24 28 48 b8 00 00 00 00 00 fc ff df
All code
========
   0:	00 48 8b             	add    %cl,-0x75(%rax)
   3:	54                   	push   %rsp
   4:	24 18                	and    $0x18,%al
   6:	48 8b 05 c3 88 a6 ec 	mov    -0x1359773d(%rip),%rax        # 0xffffffffeca688d0
   d:	48 81 c2 60 ea 00 00 	add    $0xea60,%rdx
  14:	48 39 c2             	cmp    %rax,%rdx
  17:	78 0a                	js     0x23
  19:	e8 42 0e 96 eb       	call   0xffffffffeb960e60
  1e:	e9 25 fd ff ff       	jmp    0xfffffffffffffd48
  23:	48 8d 3d 56 56 d7 ff 	lea    -0x28a9aa(%rip),%rdi        # 0xffffffffffd75680
  2a:*	67 48 0f b9 3a       	ud1    (%edx),%rdi		<-- trapping instruction
  2f:	eb e8                	jmp    0x19
  31:	48 8b 5c 24 28       	mov    0x28(%rsp),%rbx
  36:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  3d:	fc ff df 

Code starting with the faulting instruction
===========================================
   0:	67 48 0f b9 3a       	ud1    (%edx),%rdi
   5:	eb e8                	jmp    0xffffffffffffffef
   7:	48 8b 5c 24 28       	mov    0x28(%rsp),%rbx
   c:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  13:	fc ff df 
[ 2006.762171][   T12] RSP: 0018:ffa00000000c7980 EFLAGS: 00010297
[ 2006.762324][   T12] RAX: 00000001001a0927 RBX: ffa00000000c7af8 RCX: 0000000000000001
[ 2006.762515][   T12] RDX: 00000001001a0926 RSI: 0000000000000004 RDI: ffffffffc051e030
[ 2006.762699][   T12] RBP: 0000000000000001 R08: ffffffffc07a87aa R09: ffe21c00014ce81c
[ 2006.762877][   T12] R10: ffe21c00014ce81d R11: 0000000000000001 R12: dffffc0000000000
[ 2006.763058][   T12] R13: ff1100000a6740e0 R14: fffffbfff80a5607 R15: ff1100001019e800
[ 2006.763233][   T12] FS:  0000000000000000(0000) GS:ff110000b758b000(0000) knlGS:0000000000000000
[ 2006.763440][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2006.763599][   T12] CR2: 00007ffebbe26b30 CR3: 0000000077948005 CR4: 0000000000771ef0
[ 2006.763776][   T12] PKRU: 55555554
[ 2006.763866][   T12] Call Trace:
[ 2006.763957][   T12]  <TASK>
[ 2006.764021][   T12]  ? nf_conntrack_cleanup_end (net/netfilter/nf_conntrack_core.c:2488) nf_conntrack
[ 2006.764168][   T12]  ? kfree (mm/slub.c:6663 (discriminator 3) mm/slub.c:6871 (discriminator 3))
[ 2006.764254][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 (discriminator 33) kernel/locking/lockdep.c:5831 (discriminator 33))
[ 2006.764372][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129 (discriminator 4)) nf_conntrack
[ 2006.764519][   T12]  ops_undo_list (net/core/net_namespace.c:251 (discriminator 4))
[ 2006.764639][   T12]  ? netns_install (net/core/net_namespace.c:223)
[ 2006.764754][   T12]  cleanup_net (net/core/net_namespace.c:698)
[ 2006.764865][   T12]  ? process_one_work (kernel/workqueue.c:3233 (discriminator 1))
[ 2006.764983][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[ 2006.765117][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 1) kernel/rcu/tree.c:751 (discriminator 1))
[ 2006.765227][   T12]  ? process_one_work (kernel/workqueue.c:3233 (discriminator 1))
[ 2006.765336][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 (discriminator 33) kernel/locking/lockdep.c:5831 (discriminator 33))
[ 2006.765452][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 1) kernel/rcu/tree.c:751 (discriminator 1))
[ 2006.765562][   T12]  process_one_work (kernel/workqueue.c:3262)
[ 2006.765680][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3159)
[ 2006.765789][   T12]  ? lock_acquire.part.0 (kernel/locking/lockdep.c:470 kernel/locking/lockdep.c:5870)
[ 2006.765904][   T12]  ? assign_work (kernel/workqueue.c:1200)
[ 2006.766016][   T12]  worker_thread (kernel/workqueue.c:3334 (discriminator 2) kernel/workqueue.c:3421 (discriminator 2))
[ 2006.766130][   T12]  ? process_one_work (kernel/workqueue.c:3367)
[ 2006.766243][   T12]  kthread (kernel/kthread.c:463)
[ 2006.766328][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 2006.766443][   T12]  ? __lock_release.isra.0 (kernel/locking/lockdep.c:5536)
[ 2006.766553][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 1) kernel/rcu/tree.c:751 (discriminator 1))
[ 2006.766665][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 2006.766777][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[ 2006.766887][   T12]  ? arch_exit_to_user_mode_prepare.isra.0 (arch/x86/entry/syscall_64.c:37)
[ 2006.767024][   T12]  ? __switch_to (./include/linux/thread_info.h:140 (discriminator 2) arch/x86/kernel/process.h:16 (discriminator 2) arch/x86/kernel/process_64.c:676 (discriminator 2))
[ 2006.767135][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)


Finger prints:
nf_conntrack_cleanup_net_list:ops_undo_list:cleanup_net:process_one_work:worker_thread