mount.nfs4 : explanation of "retry" expiration timeout option

Issue

On the event of a non-responsive NFS server, nfs mount retry expiration timeout is declared, but we still keep trying even doubling the supposed timeout :

[root@rhel76-2 ~]# date ; time mount -v rhel73:/5GBshare /mnt ; date
Mon Sep  7 10:15:58 CEST 2020
mount.nfs: timeout set for Mon Sep  7 10:17:58 2020
mount.nfs: trying text-based options 'vers=4.1,addr=172.23.1.225,clientaddr=172.23.1.241'
mount.nfs: mount(2): Connection timed out
mount.nfs: Connection timed out

real    4m17.674s
user    0m0.012s
sys 0m0.025s
Mon Sep  7 10:20:16 CEST 2020