inotify(?) prevents disks from being unmounted

[probonopd]

inotify(?) prevents disks from being unmounted.

It should not.

Inotify watches can not prevent unmounting of filesystem. The documentation even mentions the specialized inotify event, that gets dispatched when the filesystem is unmounted: "IN_UNMOUNT - Filesystem containing watched object was unmounted". And if you were to read a tiny bit on the subject, you would discover, that inotify/fanotify have been specifically created to address issue of their predecessor dnotify, which didn't support unmounting watched directory.

Source: https://stackoverflow.com/questions/45951874/system-call-interface-to-proc-information#comment78876871_45951874

More information:
https://lwn.net/Articles/604686/

If it is not inotify, what is it then?

Interestingly this happens with the NTFS drive but not with e.g., Live ISO images written to USB disks.

[probonopd]

Actually we were just not closing files. Fixed in 3a4cf0a