======================================
| xx__-> [ 4026.576212][   T12] ------------[ cut here ]------------
| [ 4026.576862][   T12] conntrack cleanup blocked for 60s
| [ 4026.576865][   T12] WARNING: net/netfilter/nf_conntrack_core.c:2511 at nf_conntrack_cleanup_net_list+0x4a0/0x540 [nf_conntrack], CPU#3: 0/12
| [ 4026.577939][   T12] Modules linked in: xt_conntrack nf_conntrack nf_defrag_ipv4 nf_defrag_ipv6 unix_diag act_gact cls_matchall bonding psample macsec vxlan ip6_gre ip_gre gre cls_u32 sch_htb cls_flower sch_prio xt_mark sch_ingress act_mirred cls_basic sch_fq_codel xfrm_user xt_policy xt_HL nft_compat nf_tables amt [last unloaded: netdevsim]
[ 4026.580328][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 4026.580708][   T12] Workqueue: netns cleanup_net
[ 4026.581030][   T12] RIP: 0010:nf_conntrack_cleanup_net_list (net/netfilter/nf_conntrack_core.c:2511) nf_conntrack
[ 4026.581499][   T12] Code: 00 00 00 65 48 2b 05 cf 11 71 de 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 a1 e6 ff <67> 48 0f b9 3a e9 0f ff ff ff 48 c7 c7 bc 4f 88 c0 e8 7a b4 2f da
All code
========
   0:	00 00                	add    %al,(%rax)
   2:	00 65 48             	add    %ah,0x48(%rbp)
   5:	2b 05 cf 11 71 de    	sub    -0x218eee31(%rip),%eax        # 0xffffffffde7111da
   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 a1 e6 ff 	lea    -0x195e30(%rip),%rdi        # 0xffffffffffe6a1fa
  2a:*	67 48 0f b9 3a       	ud1    (%edx),%rdi		<-- trapping instruction
  2f:	e9 0f ff ff ff       	jmp    0xffffffffffffff43
  34:	48 c7 c7 bc 4f 88 c0 	mov    $0xffffffffc0884fbc,%rdi
  3b:	e8 7a b4 2f da       	call   0xffffffffda2fb4ba

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 4f 88 c0 	mov    $0xffffffffc0884fbc,%rdi
  11:	e8 7a b4 2f da       	call   0xffffffffda2fb490
[ 4026.582608][   T12] RSP: 0018:ffffc900000c7988 EFLAGS: 00010297
[ 4026.582985][   T12] RAX: 000000010038da4c RBX: ffffc900000c7ae8 RCX: ffffffffc0a0db3a
[ 4026.583475][   T12] RDX: 000000010038da4b RSI: 0000000000000004 RDI: ffffffffc0878030
[ 4026.583912][   T12] RBP: ffff888018997c20 R08: 0000000000000000 R09: ffffed1003132f84
[ 4026.584366][   T12] R10: ffff888018997c23 R11: ffffffffc0a042ba R12: 0000000000000001
[ 4026.584817][   T12] R13: ffff8880127cba00 R14: dffffc0000000000 R15: ffffc900000c79e8
[ 4026.585281][   T12] FS:  0000000000000000(0000) GS:ffff8880ce081000(0000) knlGS:0000000000000000
[ 4026.586187][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 4026.586541][   T12] CR2: 00005595adc5fac0 CR3: 0000000005740005 CR4: 0000000000772ef0
[ 4026.586955][   T12] PKRU: 55555554
[ 4026.587185][   T12] Call Trace:
[ 4026.587452][   T12]  <TASK>
[ 4026.587596][   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
[ 4026.588026][   T12]  ? nf_conntrack_cleanup_end (net/netfilter/nf_conntrack_core.c:2488) nf_conntrack
[ 4026.588383][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129) nf_conntrack
[ 4026.588732][   T12]  ? nf_conntrack_pernet_exit (net/netfilter/nf_conntrack_standalone.c:1129) nf_conntrack
[ 4026.589102][   T12]  ? _raw_spin_unlock (./arch/x86/include/asm/preempt.h:104 ./include/linux/spinlock_api_smp.h:143 kernel/locking/spinlock.c:186)
[ 4026.589414][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[ 4026.589715][   T12]  ? netns_install (net/core/net_namespace.c:223)
[ 4026.590014][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[ 4026.590306][   T12]  cleanup_net (net/core/net_namespace.c:698)
[ 4026.590593][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[ 4026.590872][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[ 4026.591178][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831)
[ 4026.591479][   T12]  process_one_work (kernel/workqueue.c:3262)
[ 4026.591822][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3159)
[ 4026.592148][   T12]  ? assign_work (kernel/workqueue.c:1200)
[ 4026.592448][   T12]  worker_thread (kernel/workqueue.c:3334 kernel/workqueue.c:3421)
[ 4026.592742][   T12]  ? bh_worker (kernel/workqueue.c:3367)
[ 4026.593051][   T12]  kthread (kernel/kthread.c:463)
[ 4026.593267][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4026.593534][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[ 4026.593819][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[ 4026.594113][   T12]  ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5831)
[ 4026.594396][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[ 4026.594687][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4026.594994][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[ 4026.595278][   T12]  ? arch_exit_to_user_mode_prepare.constprop.0 (arch/x86/entry/syscall_64.c:37)
[ 4026.595680][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[ 4026.595982][   T12]  ? __switch_to (./arch/x86/include/asm/cpufeature.h:101 arch/x86/kernel/process_64.c:377 arch/x86/kernel/process_64.c:665)
[ 4026.596292][   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