I unsafely removed a USB device that was attached to loop0 with losetup and could not delete nor detach loop0 afterwards.
losetup -a shows /dev/loop0: [0005]:145606719 (/dev/sdb1)
When I remount the device to /dev/sdb1, umount it and try losetup -d /dev/loop0, I will still get the same error loop: can't delete device /dev/loop0: Device or resource busy. Is there a way to get rid of the loop device?
Are you sure that the device isn't busy? Have you ever tried fuser to determine an possible PID?
Precautionary get all possible information:
fuser -c /dev/loop0
fuser -d /dev/loop0
fuser -f /dev/loop0
Try to stop the process, which could use /dev/loop0. If necessary use kill -9 or try fuser -k to send the kill signal -> look at man fuser.