mount lag, umounting returns wrong "Device busy"

[Harald Schmalzbauer]

 Hello,

while playing with new jail features, I recognized that manually
umounting doesn't work as I'd expect.
After jail has been destroyed, the following mountpoint is active:
    /dev/gpt/jailname1ROOT on /.jail.jailname1 (ufs, local, read-only)

There was var mounted to /.jail.jailname1/var but that sucessfully umounted.
'fstat' also shows no open files in /.jail.jailname1

But when I do 'umount /.jail.jailname' I get "Device busy" returned.
Some minutes later umounting works.
But I always have to wait some time, although nothing is open and
nothing is mounted above.

Does anybody have an idea what could cause that false "Device busy"?

-Harry

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