> on my workstation, with a low delay-to-repeat, running "umount
> /mountpoint", regardless of whether or not anything is mounted there,
> causes repeated keystrokes.
> 
> I'm guessing this happens with more than just umount...

indeed it does, sync(8) causes this to happen every time. it is
completely unacceptable on a multi-user system. I've raised this PR to
critical.