BUG #1397: busy-loop hang on web server

The following bug has been logged online:

Bug reference:      1397
Logged by:          Chris Jones
Email address:      chris@cjones.org
PostgreSQL version: 7.4.6
Operating system:   NetBSD 2.0 i386
Description:        busy-loop hang on web server
Details:

I recently upgraded my OS from a previous version.  In the process, I
recompiled PostgreSQL 7.3 (using pkgsrc).  I began seeing a hang, so I
upgraded to PostgreSQL 7.4.6 (again using pkgsrc).  Same problem still
exists:

Every day or two, PostgreSQL will hang.  It maxes out the CPU when it does,
with one process seeming to be in a busy loop.  There are the normal
auxiliary processes, as well as a zombie which I assume was servicing a
client.

The busy process doesn't respond to kill, only to "kill -KILL".  After it
dies off due to this, the others eventually (a minute or so) go away, too.

Nothing appears in errlog around the time of the hang; the only messages
there are associated with various startup operations.  The errlog does,
however, indicate the time when the server was interrupted.  That time
coincides with when a backup (using dump) was happening last night.

Please let me know what other information would be useful in debugging this.