More info on "Why can't I umount ?"

[Don Lewis]

This problem just bit me again, so I did some digging and it looks like I
found a bug.  The problem is that I am unable to unmount an nfs filesystem
on a client machine.  Umount tells me that the filesystem is busy, but
ofiles does not find any processes referencing the filesystem.

I wrote a program to snoop around in /dev/kmem, and I found that the
mi_refct field in the mntinfo structure for the the filesystem appears to
be corrupted.  The other nfs mounts have small postive reference counts,
but this one has a reference count of -9602!  There is another nfs mount
with a negative reference count (-2921) that is also unmountable.  What is
interesting is that there have been nfs write errors to both servers since
the client was last booted.  In one case the problem was a stale file
handle, in the other case the partition was full.  I am not able to
reproduce the corrupted reference counts by causing these types of write
errors on purpose.

The client is a Sun 4/280 running 4.0.3.  The two servers are a Sun 3/60
running 4.0.3 and a Sun 386i running 4.0.2.  Both the 4/280 and the 3/60
are using the NFS confused file patch.

Don "Truck" Lewis                      Harris Semiconductor
Internet:  del at mlb.semi.harris.com     PO Box 883   MS 62A-028
Phone:     (407) 729-5205              Melbourne, FL  32901