======================================
| [ 2103.316019][   T12] ------------[ cut here ]------------
| [ 2103.316427][   T12] conntrack cleanup blocked for 60s
| [ 2103.316430][   T12] WARNING: net/netfilter/nf_conntrack_core.c:2511 at nf_conntrack_cleanup_net_list+0x3da/0x550 [nf_conntrack], CPU#2: 0/12
| [ 2103.316974][   T12] Modules linked in: xt_conntrack nf_conntrack nf_defrag_ipv4 nf_defrag_ipv6 drop_monitor cls_flower cls_bpf netdevsim psample act_gact cls_matchall sch_ingress ip6t_rpfilter nft_compat nf_tables vxlan mpls_gso mpls_iptunnel mpls_router
[ 2103.318444][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 2103.318655][   T12] Workqueue: netns cleanup_net
[ 2103.318841][   T12] RIP: 0010:nf_conntrack_cleanup_net_list (net/netfilter/nf_conntrack_core.c:2511 (discriminator 16)) nf_conntrack
[ 2103.319109][   T12] Code: 00 48 8b 54 24 18 48 8b 05 b3 58 06 f4 48 81 c2 60 ea 00 00 48 39 c2 78 0a e8 42 2e fb f2 e9 25 fd ff ff 48 8d 3d 46 a6 0a 00 <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 b3 58 06 f4 	mov    -0xbf9a74d(%rip),%rax        # 0xfffffffff40658c0
   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 2e fb f2       	call   0xfffffffff2fb2e60
  1e:	e9 25 fd ff ff       	jmp    0xfffffffffffffd48
  23:	48 8d 3d 46 a6 0a 00 	lea    0xaa646(%rip),%rdi        # 0xaa670
  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 
[ 2103.319603][   T12] RSP: 0018:ffa00000000c7980 EFLAGS: 00010297
[ 2103.319806][   T12] RAX: 00000001001b825d RBX: ffa00000000c7af8 RCX: 0000000000000001
[ 2103.320048][   T12] RDX: 00000001001b825c RSI: 0000000000000004 RDI: ffffffffc0856030
[ 2103.320286][   T12] RBP: 0000000000000001 R08: ffffffffc07ab7ba R09: ffe21c0002d218f4
[ 2103.320517][   T12] R10: ffe21c0002d218f5 R11: 0000000000000001 R12: dffffc0000000000
[ 2103.320749][   T12] R13: ff1100001690c7a0 R14: fffffbfff810c607 R15: ff1100000bc84d00
[ 2103.320981][   T12] FS:  0000000000000000(0000) GS:ff110000b64f3000(0000) knlGS:0000000000000000
[ 2103.321261][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2103.321465][   T12] CR2: 00007fb09df9a000 CR3: 0000000064548002 CR4: 0000000000771ef0
[ 2103.321699][   T12] PKRU: 55555554
[ 2103.321843][   T12] Call Trace:
[ 2103.321985][   T12]  <TASK>
[ 2103.322117][   T12]  ? nf_conntrack_cleanup_end (net/netfilter/nf_conntrack_core.c:2488) nf_conntrack
[ 2103.322324][   T12]  ? kfree (mm/slub.c:6670 (discriminator 3) mm/slub.c:6878 (discriminator 3))
[ 2103.322466][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 (discriminator 33) kernel/locking/lockdep.c:5831 (discriminator 33))
[ 2103.322640][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129 (discriminator 4)) nf_conntrack
[ 2103.322850][   T12]  ops_undo_list (net/core/net_namespace.c:251 (discriminator 4))
[ 2103.323037][   T12]  ? netns_install (net/core/net_namespace.c:223)
[ 2103.323216][   T12]  cleanup_net (net/core/net_namespace.c:698)
[ 2103.323388][   T12]  ? process_one_work (kernel/workqueue.c:3233 (discriminator 1))
[ 2103.323560][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[ 2103.323734][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 1) kernel/rcu/tree.c:751 (discriminator 1))
[ 2103.323910][   T12]  ? process_one_work (kernel/workqueue.c:3233 (discriminator 1))
[ 2103.324093][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 (discriminator 33) kernel/locking/lockdep.c:5831 (discriminator 33))
[ 2103.324275][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 1) kernel/rcu/tree.c:751 (discriminator 1))
[ 2103.324446][   T12]  process_one_work (kernel/workqueue.c:3262)
[ 2103.324619][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3159)
[ 2103.324789][   T12]  ? lock_acquire.part.0 (kernel/locking/lockdep.c:470 kernel/locking/lockdep.c:5870)
[ 2103.324961][   T12]  ? assign_work (kernel/workqueue.c:1200)
[ 2103.325149][   T12]  worker_thread (kernel/workqueue.c:3334 (discriminator 2) kernel/workqueue.c:3421 (discriminator 2))
[ 2103.325325][   T12]  ? process_one_work (kernel/workqueue.c:3367)
[ 2103.325498][   T12]  kthread (kernel/kthread.c:463)
[ 2103.325640][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 2103.325815][   T12]  ? __lock_release.isra.0 (kernel/locking/lockdep.c:5536)
[ 2103.325986][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 (discriminator 1) kernel/rcu/tree.c:751 (discriminator 1))
[ 2103.326178][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 2103.326348][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[ 2103.326520][   T12]  ? arch_exit_to_user_mode_prepare.isra.0 (arch/x86/entry/syscall_64.c:37)
[ 2103.326724][   T12]  ? __switch_to (./arch/x86/include/asm/cpufeature.h:101 arch/x86/kernel/process_64.c:377 arch/x86/kernel/process_64.c:665)
[ 2103.326898][   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