======================================
| xx__-> [ 4101.130953][   T12] ------------[ cut here ]------------
| [ 4101.131440][   T12] conntrack cleanup blocked for 60s
| [ 4101.131443][   T12] WARNING: net/netfilter/nf_conntrack_core.c:2511 at nf_conntrack_cleanup_net_list+0x4a0/0x540 [nf_conntrack], CPU#3: 0/12
| [ 4101.132396][   T12] Modules linked in: xt_conntrack xt_length act_ct nf_flow_table nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 cls_flower unix_diag act_gact cls_matchall sch_ingress bonding psample xfrm_user macsec ip6_gre ip_gre gre cls_u32 sch_htb ipt_REJECT nf_reject_ipv4 ip6t_rpfilter nft_compat nf_tables vxlan mpls_gso mpls_iptunnel mpls_router [last unloaded: netdevsim]
[ 4101.134787][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 4101.135130][   T12] Workqueue: netns cleanup_net
[ 4101.135417][   T12] RIP: 0010:nf_conntrack_cleanup_net_list (net/netfilter/nf_conntrack_core.c:2511) nf_conntrack
[ 4101.135841][   T12] Code: 00 00 00 65 48 2b 05 cf d1 34 f0 0f 85 a0 00 00 00 48 81 c4 c0 00 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8d 3d d0 c1 db ff <67> 48 0f b9 3a e9 0f ff ff ff 48 c7 c7 bc bf 59 c0 e8 5a 76 f3 eb
All code
========
   0:	00 00                	add    %al,(%rax)
   2:	00 65 48             	add    %ah,0x48(%rbp)
   5:	2b 05 cf d1 34 f0    	sub    -0xfcb2e31(%rip),%eax        # 0xfffffffff034d1da
   b:	0f 85 a0 00 00 00    	jne    0xb1
  11:	48 81 c4 c0 00 00 00 	add    $0xc0,%rsp
  18:	5b                   	pop    %rbx
  19:	5d                   	pop    %rbp
  1a:	41 5c                	pop    %r12
  1c:	41 5d                	pop    %r13
  1e:	41 5e                	pop    %r14
  20:	41 5f                	pop    %r15
  22:	c3                   	ret
  23:	48 8d 3d d0 c1 db ff 	lea    -0x243e30(%rip),%rdi        # 0xffffffffffdbc1fa
  2a:*	67 48 0f b9 3a       	ud1    (%edx),%rdi		<-- trapping instruction
  2f:	e9 0f ff ff ff       	jmp    0xffffffffffffff43
  34:	48 c7 c7 bc bf 59 c0 	mov    $0xffffffffc059bfbc,%rdi
  3b:	e8 5a 76 f3 eb       	call   0xffffffffebf3769a

Code starting with the faulting instruction
===========================================
   0:	67 48 0f b9 3a       	ud1    (%edx),%rdi
   5:	e9 0f ff ff ff       	jmp    0xffffffffffffff19
   a:	48 c7 c7 bc bf 59 c0 	mov    $0xffffffffc059bfbc,%rdi
  11:	e8 5a 76 f3 eb       	call   0xffffffffebf37670
[ 4101.136967][   T12] RSP: 0000:ffffc900000c7988 EFLAGS: 00010297
[ 4101.137314][   T12] RAX: 000000010039fd9b RBX: ffffc900000c7ae8 RCX: ffffffffc07d2b3a
[ 4101.137810][   T12] RDX: 000000010039fd9a RSI: 0000000000000004 RDI: ffffffffc058f030
[ 4101.138317][   T12] RBP: ffff88800924c3e0 R08: 0000000000000000 R09: ffffed100124987c
[ 4101.138820][   T12] R10: ffff88800924c3e3 R11: ffffffffc07c92ba R12: 0000000000000001
[ 4101.139269][   T12] R13: ffff888013968100 R14: dffffc0000000000 R15: ffffc900000c79e8
[ 4101.139670][   T12] FS:  0000000000000000(0000) GS:ffff8880bc680000(0000) knlGS:0000000000000000
[ 4101.140144][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 4101.140839][   T12] CR2: 000056274099e070 CR3: 0000000022d45002 CR4: 0000000000772ef0
[ 4101.141345][   T12] PKRU: 55555554
[ 4101.141596][   T12] Call Trace:
[ 4101.141845][   T12]  <TASK>
[ 4101.142028][   T12]  ? nf_conntrack_cleanup_net_list (./include/linux/rcupdate.h:331 ./include/linux/rcupdate.h:867 ./include/net/netns/generic.h:45 ./include/net/netfilter/nf_conntrack.h:369 net/netfilter/nf_conntrack_core.c:2503) nf_conntrack
[ 4101.142542][   T12]  ? nf_conntrack_cleanup_end (net/netfilter/nf_conntrack_core.c:2488) nf_conntrack
[ 4101.142974][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129) nf_conntrack
[ 4101.143400][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129) nf_conntrack
[ 4101.143820][   T12]  ? _raw_spin_unlock (./arch/x86/include/asm/preempt.h:104 ./include/linux/spinlock_api_smp.h:143 kernel/locking/spinlock.c:186)
[ 4101.144132][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[ 4101.144406][   T12]  ? netns_install (net/core/net_namespace.c:223)
[ 4101.144704][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[ 4101.145049][   T12]  cleanup_net (net/core/net_namespace.c:698)
[ 4101.145336][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[ 4101.145605][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[ 4101.145882][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831)
[ 4101.146161][   T12]  process_one_work (kernel/workqueue.c:3262)
[ 4101.146442][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3159)
[ 4101.146717][   T12]  ? assign_work (kernel/workqueue.c:1200)
[ 4101.147073][   T12]  worker_thread (kernel/workqueue.c:3334 kernel/workqueue.c:3421)
[ 4101.147412][   T12]  ? bh_worker (kernel/workqueue.c:3367)
[ 4101.147748][   T12]  kthread (kernel/kthread.c:463)
[ 4101.148004][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4101.148294][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[ 4101.148630][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[ 4101.148944][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831)
[ 4101.149217][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[ 4101.149488][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4101.149756][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[ 4101.150035][   T12]  ? arch_exit_to_user_mode_prepare.constprop.0 (arch/x86/entry/syscall_64.c:37)
[ 4101.150426][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4101.150755][   T12]  ? __switch_to (./arch/x86/include/asm/cpufeature.h:101 arch/x86/kernel/process_64.c:377 arch/x86/kernel/process_64.c:665)
[ 4101.151076][   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