device-mapper: remove ioctl on luks-xxxx failed: Device or resource busy

After two years of fighting with this, I think I've finally cracked it completely!

dmsetup ls gives you the data you need:

$ sudo dmsetup ls
luks-xxxxx (252:1)

then

sudo lsof |grep 252,1

It seems that sudo may be critical here -- at least in some cases.

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This should give you the information necessary to close all open files on the device -- including names of open files and process IDs for the offending applications. You may be able to simply go to those apps and close them, but a brute force approach might be something like:

kill -9 (process ID)

Once you've closed all the files, some of the command-line tools shown in the question may be necessary in order to close down the existing mount before it can be reopened normally.

Try to stop LVM group prior to stop cypher:

lvchange -a n [LVM_Group_name]

then

cryptsetup -v luksClose [LUKS_name]

Sample:

lvchange -a n My_vg_crypt
cryptsetup -v luksClose My_Crypt

next time try a lazy umount

umount -l /<folder>

This works for me most of the times, especially useful with hung-up NFS-drives.