mount LABEL=ACME /mnt/acme
mount: /dev/sdc5 already mounted or /mnt/acme busy

strace and Google help me to solve this issue:

There's a cache file /etc/blkid/blkid.tab where information about block devices (labels, uuid) are stored. To solve/avoid this issue, just refresh this cache file:

  • remove/backup the file
  • regenerate it by running blkid command


Doing so, label will be found/used on multipath device first when mounting from label.