macOS failing on umount?

[mgree]

~~My macOS CI spontaneously failed on its cronjob run. (More bad news after the forced downgrade to 10.15!)~~ Edit: this turned out to be a spurious failure. Even so, there does seem to be some sort of warning on macOS on umount.

So far as I can tell, we're getting an EPERM after unmount. Here's a representative point in the logs:

https://github.com/mgree/ffs/runs/5095412110?check_suite_focus=true#step:5:26037

Have you (or other users of fuser on Mac) had this problem? Nothing's changed in my setup...