======================================
| xx__-> [ 4133.679229][   T12] ------------[ cut here ]------------
| [ 4133.679838][   T12] conntrack cleanup blocked for 60s
| [ 4133.679842][   T12] WARNING: net/netfilter/nf_conntrack_core.c:2511 at 0x0, CPU#3: kworker/u16:0/12
| [ 4133.680757][   T12] Modules linked in: xt_conntrack xfrm_interface xfrm_user nft_chain_nat xt_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 cls_matchall sch_prio xt_mark nft_compat nf_tables act_mirred cls_basic sch_fq_codel act_gact cls_flower sch_ingress vxlan
[ 4133.682778][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 4133.683186][   T12] Workqueue: netns cleanup_net
[ 4133.683490][   T12] RIP: 0010:nf_conntrack_cleanup_net_list (net/netfilter/nf_conntrack_core.c:2511) nf_conntrack
[ 4133.684091][   T12] Code: 00 00 00 65 48 2b 05 ff 81 9b fc 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 72 d8 ff <67> 48 0f b9 3a e9 0f ff ff ff 48 c7 c7 bc 3f 4e c0 e8 0a bf 59 f8
All code
========
   0:	00 00                	add    %al,(%rax)
   2:	00 65 48             	add    %ah,0x48(%rbp)
   5:	2b 05 ff 81 9b fc    	sub    -0x3647e01(%rip),%eax        # 0xfffffffffc9b820a
   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 72 d8 ff 	lea    -0x278e00(%rip),%rdi        # 0xffffffffffd8722a
  2a:*	67 48 0f b9 3a       	ud1    (%edx),%rdi		<-- trapping instruction
  2f:	e9 0f ff ff ff       	jmp    0xffffffffffffff43
  34:	48 c7 c7 bc 3f 4e c0 	mov    $0xffffffffc04e3fbc,%rdi
  3b:	e8 0a bf 59 f8       	call   0xfffffffff859bf4a

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 3f 4e c0 	mov    $0xffffffffc04e3fbc,%rdi
  11:	e8 0a bf 59 f8       	call   0xfffffffff859bf20
[ 4133.685223][   T12] RSP: 0018:ffffc900000c7988 EFLAGS: 00010297
[ 4133.685567][   T12] RAX: 00000001003a7cce RBX: ffffc900000c7ae8 RCX: ffffffffc074fb0a
[ 4133.685977][   T12] RDX: 00000001003a7ccd RSI: 0000000000000004 RDI: ffffffffc04d7030
[ 4133.686389][   T12] RBP: ffff888012adcda0 R08: 0000000000000000 R09: ffffed100255b9b4
[ 4133.686797][   T12] R10: ffff888012adcda3 R11: ffff888001abd090 R12: 0000000000000001
[ 4133.687209][   T12] R13: ffff88800c898700 R14: dffffc0000000000 R15: ffffc900000c79e8
[ 4133.687629][   T12] FS:  0000000000000000(0000) GS:ffff8880b0098000(0000) knlGS:0000000000000000
[ 4133.688600][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 4133.688942][   T12] CR2: 00007fbb8f19b760 CR3: 000000001af45002 CR4: 0000000000772ef0
[ 4133.689360][   T12] PKRU: 55555554
[ 4133.689568][   T12] Call Trace:
[ 4133.689770][   T12]  <TASK>
[ 4133.689920][   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
[ 4133.690348][   T12]  ? nf_conntrack_cleanup_end (net/netfilter/nf_conntrack_core.c:2488) nf_conntrack
[ 4133.690693][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129) nf_conntrack
[ 4133.691044][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129) nf_conntrack
[ 4133.691393][   T12]  ? _raw_spin_unlock (./arch/x86/include/asm/preempt.h:104 ./include/linux/spinlock_api_smp.h:143 kernel/locking/spinlock.c:186)
[ 4133.691670][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[ 4133.691956][   T12]  ? netns_install (net/core/net_namespace.c:223)
[ 4133.692240][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[ 4133.692517][   T12]  cleanup_net (net/core/net_namespace.c:698)
[ 4133.692785][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[ 4133.693053][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[ 4133.693336][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831)
[ 4133.693607][   T12]  process_one_work (kernel/workqueue.c:3262)
[ 4133.693888][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3159)
[ 4133.694177][   T12]  ? assign_work (kernel/workqueue.c:1200)
[ 4133.694451][   T12]  worker_thread (kernel/workqueue.c:3334 kernel/workqueue.c:3421)
[ 4133.694727][   T12]  ? bh_worker (kernel/workqueue.c:3367)
[ 4133.694994][   T12]  kthread (kernel/kthread.c:463)
[ 4133.695207][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4133.695512][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[ 4133.695840][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[ 4133.696175][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831)
[ 4133.696467][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[ 4133.696802][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4133.697116][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[ 4133.697392][   T12]  ? arch_exit_to_user_mode_prepare.constprop.0 (arch/x86/entry/syscall_64.c:37)
[ 4133.697789][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4133.698053][   T12]  ? __switch_to (./include/linux/thread_info.h:140 arch/x86/kernel/process.h:16 arch/x86/kernel/process_64.c:676)
[ 4133.698345][   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