RHEL7, NFSD : opening a file for writing may return EWOULDBLOCK/EAGAIN

Issue

When opening a file for writing on NFS server, it may return EWOULDBLOCK/EAGAIN on first attempt :

[root@rhel73 ~]# grep -i lease /proc/locks 
24: LEASE  ACTIVE    READ  21013 fc:31:51 0 EOF
[root@rhel73 ~]# cp /5GBshare/kk /5GBshare/testfile
cp: overwrite ‘/5GBshare/testfile’? y
cp: cannot create regular file ‘/5GBshare/testfile’: Resource temporarily unavailable
[root@rhel73 ~]# grep -i lease /proc/locks

Error code is produced on open syscall :

22132 06:49:55.307716 open("/5GBshare/testfile", O_WRONLY|O_TRUNC) = -1 EAGAIN (Resource temporarily unavailable) <0.001289>