umount() taking minutes for FUSE filesystems

[Nikolaus Rath]

Hello,

It seems that in some situations, the unmount() system call takes
minutes to unmount fuse filesystems. To reproduce, download a Git
snapshot of libfuse 3 from https://github.com/libfuse/libfuse and do:

$ md build; cd build
$ meson ..
$ mesonconf -D buildtype=debug # optional
$ ninja

Then execute examples/printcap. This will take very long, and all the
time is spent in the unmount(mountpoint, MNT_FORCE) call in
mount_bsd.c:fuse_kern_unmount().

Does anyone have an idea what might be causing this and how to fix it?

My hunch is that it has something to do with libfuse no longer
responding to requests at this point. But I'm at my wits end as to why
and what to do about it....

Best,
-Nikolaus

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