mount -a always tries to mount CIFS share subdir despite being already mounted

Issue

• Running mount -a several times causes mount attempts of CIFS shares subdir, included in fstab even though they are already mounted :

[root@rhel74-2 tmp]# grep cifs /etc/fstab
//rhel73/myshare/mydir  /mnt/mnt2   cifs    credentials=/etc/fstab.d/cifs/myshare,uid=1000,gid=1000,dir_mode=0777,file_mode=0666 0       0
[root@rhel74-2 tmp]# grep cifs /proc/mounts 
//rhel73/myshare/mydir /mnt/mnt2 cifs rw,relatime,vers=1.0,cache=strict,username=roberto,domain=RHEL73,uid=1000,forceuid,gid=1000,forcegid,addr=172.23.1.225,file_mode=0666,dir_mode=0777,nounix,serverino,mapposix,rsize=61440,wsize=65536,echo_interval=60,actimeo=1 0 0
[root@rhel74-2 tmp]# df -k -t cifs
Filesystem             1K-blocks    Used Available Use% Mounted on
//rhel73/myshare/mydir   8374272 7982708    391564  96% /mnt/mnt2
[root@rhel74-2 tmp]# mount -vvv -a
/                        : ignored
/boot                    : already mounted
swap                     : ignored
/mnt                     : already mounted
mount.cifs kernel mount options: ip=172.23.1.225,unc=\\rhel73\myshare,dir_mode=0777,file_mode=0666,uid=1000,gid=1000,user=roberto,prefixpath=mydir,pass=********
mount error(16): Device or resource busy
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
[root@rhel74-2 tmp]# mount -vvv -a
/                        : ignored
/boot                    : already mounted
swap                     : ignored
/mnt                     : already mounted
mount.cifs kernel mount options: ip=172.23.1.225,unc=\\rhel73\myshare,dir_mode=0777,file_mode=0666,uid=1000,gid=1000,user=roberto,prefixpath=mydir,pass=********
mount error(16): Device or resource busy
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

• You may get EBUSY or a successful mount depending on CIFS client/server setup (in this latter case, a successful mount, /proc/mounts gets duplicate entries each time mount -a runs) but mount is always attempted.