======================================
| xx__-> [ 3730.251954][   T12] ------------[ cut here ]------------
| [ 3730.252680][   T12] conntrack cleanup blocked for 60s
| [ 3730.252684][   T12] WARNING: net/netfilter/nf_conntrack_core.c:2511 at 0x0, CPU#0: kworker/u16:0/12
| [ 3730.253458][   T12] Modules linked in: xt_conntrack drop_monitor act_gact cls_flower sctp_diag sctp nft_chain_nat xt_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 bonding xfrm_user macsec vxlan ip6_gre ip_gre gre cls_u32 sch_htb cls_bpf sch_ingress netdevsim psample ip6t_REJECT nf_reject_ipv6 nft_compat nf_tables
[ 3730.255835][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 3730.256258][   T12] Workqueue: netns cleanup_net
[ 3730.256605][   T12] RIP: 0010:nf_conntrack_cleanup_net_list (net/netfilter/nf_conntrack_core.c:2511) nf_conntrack
[ 3730.257132][   T12] Code: 00 00 00 65 48 2b 05 ff d1 73 e8 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 00 92 15 00 <67> 48 0f b9 3a e9 0f ff ff ff 48 c7 c7 bc 0f 93 c0 e8 0a 0f 32 e4
All code
========
   0:	00 00                	add    %al,(%rax)
   2:	00 65 48             	add    %ah,0x48(%rbp)
   5:	2b 05 ff d1 73 e8    	sub    -0x178c2e01(%rip),%eax        # 0xffffffffe873d20a
   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 00 92 15 00 	lea    0x159200(%rip),%rdi        # 0x15922a
  2a:*	67 48 0f b9 3a       	ud1    (%edx),%rdi		<-- trapping instruction
  2f:	e9 0f ff ff ff       	jmp    0xffffffffffffff43
  34:	48 c7 c7 bc 0f 93 c0 	mov    $0xffffffffc0930fbc,%rdi
  3b:	e8 0a 0f 32 e4       	call   0xffffffffe4320f4a

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 0f 93 c0 	mov    $0xffffffffc0930fbc,%rdi
  11:	e8 0a 0f 32 e4       	call   0xffffffffe4320f20
[ 3730.258251][   T12] RSP: 0018:ffffc900000c7988 EFLAGS: 00010297
[ 3730.258684][   T12] RAX: 00000001003454db RBX: ffffc900000c7ae8 RCX: ffffffffc07cab0a
[ 3730.259135][   T12] RDX: 00000001003454da RSI: 0000000000000004 RDI: ffffffffc0924030
[ 3730.259631][   T12] RBP: ffff888005e74e60 R08: 0000000000000000 R09: ffffed1000bce9cc
[ 3730.260157][   T12] R10: ffff888005e74e63 R11: ffff888001abd090 R12: 0000000000000001
[ 3730.260635][   T12] R13: ffff88801213d600 R14: dffffc0000000000 R15: ffffc900000c79e8
[ 3730.261111][   T12] FS:  0000000000000000(0000) GS:ffff8880c4118000(0000) knlGS:0000000000000000
[ 3730.261664][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3730.262667][   T12] CR2: 00007f3d1d754900 CR3: 000000001d745004 CR4: 0000000000772ef0
[ 3730.263197][   T12] PKRU: 55555554
[ 3730.263403][   T12] Call Trace:
[ 3730.263603][   T12]  <TASK>
[ 3730.263744][   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
[ 3730.264186][   T12]  ? nf_conntrack_cleanup_end (net/netfilter/nf_conntrack_core.c:2488) nf_conntrack
[ 3730.264595][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129) nf_conntrack
[ 3730.265028][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129) nf_conntrack
[ 3730.265395][   T12]  ? _raw_spin_unlock (./arch/x86/include/asm/preempt.h:104 ./include/linux/spinlock_api_smp.h:143 kernel/locking/spinlock.c:186)
[ 3730.265738][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[ 3730.266092][   T12]  ? netns_install (net/core/net_namespace.c:223)
[ 3730.266413][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[ 3730.266743][   T12]  cleanup_net (net/core/net_namespace.c:698)
[ 3730.267077][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[ 3730.267346][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[ 3730.267678][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831)
[ 3730.268021][   T12]  process_one_work (kernel/workqueue.c:3262)
[ 3730.268359][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3159)
[ 3730.268691][   T12]  ? assign_work (kernel/workqueue.c:1200)
[ 3730.269028][   T12]  worker_thread (kernel/workqueue.c:3334 kernel/workqueue.c:3421)
[ 3730.269348][   T12]  ? bh_worker (kernel/workqueue.c:3367)
[ 3730.269652][   T12]  kthread (kernel/kthread.c:463)
[ 3730.269901][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 3730.270246][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[ 3730.270528][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[ 3730.270857][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831)
[ 3730.271196][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[ 3730.271522][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 3730.271851][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[ 3730.272182][   T12]  ? arch_exit_to_user_mode_prepare.constprop.0 (arch/x86/entry/syscall_64.c:37)
[ 3730.272622][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 3730.272967][   T12]  ? __switch_to (./include/linux/thread_info.h:140 arch/x86/kernel/process.h:16 arch/x86/kernel/process_64.c:676)
[ 3730.273293][   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