Questions about NFS3 NLM£¬NSM lock error£º

touch f1£»
exec 200>f1;
flock -xn 200

[error: on lock available ]

Server nfs-ganesha log:
nsm_monitor :Can not monitor ::ffff:10.10.10.102 SM_MON ret 5 : RPC: Timed out

client rpcdebug log :
Jul 13 15:28:51 cu09 kernel: lockd: get host 10.10.10.212
Jul 13 15:28:51 cu09 kernel: lockd: get host 10.10.10.212
Jul 13 15:28:51 cu09 kernel: lockd: nsm_monitor(10.10.10.212)
Jul 13 15:28:51 cu09 kernel: lockd: call procedure 2 on 10.10.10.212
Jul 13 15:28:51 cu09 kernel: lockd: nlm_bind_host 10.10.10.212 (10.10.10.212)
Jul 13 15:28:51 cu09 kernel: lockd: next rebind in 60000 jiffies
Jul 13 15:29:16 cu09 kernel: lockd: server returns status 2
Jul 13 15:29:16 cu09 kernel: lockd: release client host 10.10.10.212
Jul 13 15:29:16 cu09 kernel: lockd: release client host 10.10.10.212
Jul 13 15:29:16 cu09 kernel: lockd: clnt proc returns -37

What is the cause of the above?

¡¾Client¡¿
[root@fat01 ~]# uname -a
Linux fat01 3.10.0-862.el7.x86_64 #1 SMP Fri Apr 20 16:44:24 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
[root@fat01 ~]#
[root@fat01 ~]# lsb_release -a
LSB Version: :core-4.1-amd64:core-4.1-noarch:cxx-4.1-amd64:cxx-4.1-noarch:desktop-4.1-amd64:desktop-4.1-noarch:languages-4.1-amd64:languages-4.1-noarch:printing-4.1-amd64:printing-4.1-noarch
Distributor ID: CentOS
Description: CentOS Linux release 7.5.1804 (Core)
Release: 7.5.1804
Codename: Core

root@fat01 ~]# rpm -qa|grep nfs
texlive-psnfss-svn23394.9.2a-38.el7.noarch
libnfsidmap-0.25-19.el7.x86_64
nfs-utils-1.3.0-0.54.el7.x86_64
texlive-mfnfss-svn19410.0-38.el7.noarch
nfs4-acl-tools-0.3.3-17.el7.x86_64
[root@fat01 ~]# rpm -qa|grep rpc
xmlrpc-c-client-1.32.5-1905.svn2451.el7.x86_64
xmlrpc-c-1.32.5-1905.svn2451.el7.x86_64
rpcbind-0.2.0-44.el7.x86_64
libtirpc-0.2.4-0.10.el7.x86_64
kdepimlibs-kxmlrpcclient-4.10.5-4.el7.x86_64
¡¾server¡¿
ganesha:NFS-Ganesha Release = V2.7.3