With multiple LTFS mounted sometimes unmounts fail until another one is unmounted

[tomaz-beltram]

Describe the bug When using multiple LTFS mounts in parallel it happens sometimes that the unmount returns "Device or resource busy" error repeatedly for a longer period of time. Also lsof shows that the ltfs process holds open handle for a file on that mountpoint. After another LTFS is successfully unmounted all other also succeeds to unmount. It looks like a handle leak in LTFS/FUSE code. Strange thing is that all parallel LTFS mounts are somehow interrelated.

To Reproduce Steps to reproduce the behavior:

1. Mount at least two LTFS tapes in parallel
2. Start copying data from all mountpoints.
3. Finish copying on first mountpoint and issue unmount while other mounpoints are still copying data.
4. See error

Expected behavior The first LTFS is unmounted w/o error regardless of the other still being busy.

Desktop (please complete the following information):

• OS: Ubuntu 22.04

Additional context Data on tape are several 1GB files.