can not remount an FS read-only

[Mikhail Teterin]

Hello!

My /opt filesystem (playing both LOCALBASE and X11BASE) is normally
mounted read-only (not so much for security even, as for safety).

When I add/remove ports, I remount it read-write:

	mount -orw -u /opt

do, what I need and then remount it back `ro'.

This works most of the times, but sometimes, like today (after /opt was
"open" for some time), mount responds with EBUSY:

	mount: /dev/da0s2f: Device busy

According to fstat, out of 134 files opened under /opt:

	fstat | fgrep -c /opt
	134

NONE is opened for writing:

	fstat | fgrep /opt | grep -c 'w$'
	0

Is there a bug in the open-file counter somewhere, or is fstat not
telling me the whole story? In the past, trying to force the read-only
mount (-f) caused quite a few processes to segfault (sometimes including
X-server).

Thanks!

	-mi

P.S. I've seen this on both 4- and 5-stable.