Unmount failed... but had no reason to do so

[dmigowski]

fstransform version 0.9.3 - conversion of reiserfs to ext3 on Debian 10. Somewhere at the beginning I get:

12:03:32 fsmove: progress: 88.0% done,   2.4 gigabytes still to move, estimated 15 seconds left
12:03:37 fsmove: progress: 90.0% done,   2.0 gigabytes still to move, estimated 20 seconds left
12:03:37 fsmove: job completed.
12:03:37 fstransform: unmounting and running '/sbin/fsck' (disk check) on loop file '/tmp/fstransform.mount.17211/.fstransform.loop.17211'
12:03:46 fsck: fsck from util-linux 2.33.1
12:03:47 fsck: /dev/loop0: 182167/2436448 Dateien (0.3% nicht zusammenhängend), 5160437/9744640 Blöcke
12:03:47 fstransform: disconnected loop device '/dev/loop0' from file '/tmp/fstransform.mount.17211/.fstransform.loop.17211'
12:03:47 fstransform: unmounting device '/dev/sda3' before disk check
12:03:47 umount: /tmp/fstransform.mount.17211: target is busy.

12:03:47 ERROR! fstransform: command '/bin/umount /dev/sda3' failed (exit status 32)
                this is potentially a problem.
                you can either quit now by pressing ENTER or CTRL+C,

                or, if you know what went wrong, you can fix it yourself,
                then manually run the command '/bin/umount /dev/sda3'
                (or something equivalent)
                and finally resume this script by typing CONTINUE and pressing ENTER:

Went into another shell, did the umount manually, and it worked without problems. The target wasn't busy anymore. Maybe one should add a small wait loop here or wait until the previously started processes operating on the filesystem are really stopped.