"mount -u -o ro" problems with 7-stable

[Oliver Fromme]

Hi,

This happened to me repeatedly (but not always), even
after updating to the latest RELENG_7 yesterday ...

1. Boot into single user mode
2. fsck /    # finishes successful!
3. mount -u /
4. Do a few edits to files in /etc
5. mount -u -o ro /
softdep_waitidle: Failed to flush worklist for 0xc1f36b30
mount: /dev/ad0s1a : Device busy

I can't remount the root file system read-only, so I'm
forced to type "reboot" and go to single-user mode again.
At this point the root file system is dirty and fsck
needs to be run to fix it.

The same happens sometimes when going from multi-user to
single-user ("shutdown now") and trying to unmount /usr.
Sometimes it works, sometimes it fails the same way as
above.

Another thing I noticed:  When remounting the root FS
to read-only works, and I try to fsck it afterwards,
I get this:

** /dev/ad0s1a (NO WRITE)

So it refuses to fix anything, even though the FS is not
mounted read-write.  I'm not sure if this is expected
behaviour, but it was my understanding that fsck should
be able to fix file systems that are mounted read-only.

All of that is with a recent 7-stable (20081016) on an
ASUS notebook that works very well otherwise.  Well,
except that it's not supported by acpi_asus(4) even
though the manpage claims it is, but that's probably
unrelated to the softdep_waitidle problem.

Best regards
   Oliver

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