Weird Linux - FreeBSD/ZFS NFSv4 interoperability problem

[David Brodbeck]

(Note: I originally posted this to freebsd-questions, and it was
suggested I take it here.)

While doing some interoperability testing between Linux and FreeBSD, I
came up with this unusual issue.  I could use some help figuring out
if this is a bug, and if so, where to file it.  Here's the scenario:

- FreeBSD 8.1-RELEASE server, sharing a ZFS filesystem via NFSv4.
- Linux client (I've tested with RHEL 5.4 and Debian Lenny) mounting
said filesystem with NFSv4.
- A user on the Linux client does a Subversion checkout onto the
mounted filesystem.

At the end of the checkout, access to the filesystem hangs.  nfsd on
the FreeBSD server and rpciod on the Linux client seem to be in a
tight loop, and there's lots of network traffic between them.  I can
reproduce this every time.

The problem does not occur if the backing filesystem is UFS instead of
ZFS, if NFSv3 is used instead of NFSv4, or if the client is FreeBSD
instead of Linux.