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(at)cjones(dot)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.