Quoting Thomas Eberhardt,

> Since a few day I've trouble to shutdown my machine (running 
> NetBSD-current/i386). Sometimes it just hangs on the "Syncing disks"
> kernel message. Escaping to the kernel debugger and doing "ps"
> shows that "mfs" is still there (I use an mfs as /tmp).
> Perhaps this has something to do with "vfs_unmountall"?

Yes, I have seen problems too. With the latest kernels (april 14-15th)
I sometimes get panics when rebooting. This happens after using the 'reboot'
command. The pannic message is "vinvalbuf: dirty bufs" (which is from
kern/vfs_subr.c), and the call history is (according to ddb):

vinvalbuf()
spec_close()
ffs_unmount()
doumount()
vfs_unmountall()
boot()
reboot()

This is on a 486 with 2 IDE disks (though I don't think that matters
much here).

- Frank