ffs_truncate3 panics

Hi,

During testing of the pNFS server I get an ffs_truncate3 panic every once in a while.
A few things that might be relevant:
- Seems to happen more often when soft update journaling is enabled, but will
  happen when it is disabled.
- Normally happens when a fairly large subtree of the file system is being removed.

These file systems are a bit odd, since all the regular files in them are empty but
have extended attributes that are accessed during the subtree removal. (The
extended attributes tell the server where the data files are.)

I replaced the panic() with a printf() and every time the printf() happens...
bo->bo_dirty.bv_cnt == 0 and bo->bo_clean.bv_cnt == 1.
After one of these printf()s, the system continues to run ok. When the file
system is fsck'd after this has occurred, it passes fine and I haven't seen and
indication of file system corruption after running with this file system for
quite a while after the printf()s first occurred.

Since the panic() only occurs when "options INVARIANTS" is enabled and I don't
see evidence of file system corruption, I'm wondering if this panic() is valid and
needed?

rick