Radeon 9200 hangs: How to debug?

[Randall Nortman]

I've got an Athlon64 system with a Sapphire Radeon 9200 (64MB, using
DVI output), running X.org version 6.8.0 on Gentoo.  (Gentoo has not
released 6.8.1 packages yet.)  I'm using the open-source drivers, not
the ATI proprietary drivers.

X starts just fine and works most of the time.  Occasionally, and
completely unpredictably, the X server will hang.  I cannot switch to
a virtual console with Ctrl-Alt-F1 as I ought to be able to.  There's
no cursor movement and no windows are updating.  Sometimes this
happens while the screensaver is running; sometimes it happens when
I'm just typing into a terminal window; sometimes it happens while I'm
moving the mouse; sometimes it happens while I'm playing ut2k4.  It
doesn't happen at any particular time of day or with any sort of
regularity, or when system load is particularly high or particularly
low.  It seems to be completely random.

When it happens, I can ssh in from another system.  When I do so, I
always find that the X process is consuming 100% of CPU time.  I
usually cannot kill it, not even with 'kill -9'.  (Once, I was able to
kill it and start a new X server, but most of the time this does not
work.)  The only solution is to reboot the system (remotely, since
Ctrl-Alt-Del does not work from the console while X is hung).  When I
do so, the screen continues to display whatever was last on screen
right up until the box physically resets and then the BIOS display
comes up and the box boots normally.

There is nothing unusual in the logs when this happens.  There's no
core dump, obviously.  I would like to be able to create a useful bug
report about this, but I'm afraid I can't even begin to provide any
useful information.  How do we debug problems like this?  Can X be
compiled with extra debugging code?  Would that greatly slow down
performance?  (Since I cannot reproduce the bug at will, I will need
to just continue to use the system as normal until it hangs.  If the
system is quite slow because of debugging code, that will be quite
annoying.)

Should I perhaps start turning off features until the system becomes
stable?  You can see in the log that I have quite a few
modules/extensions loaded, including dbe, XVideo, glx, dri, drm,
RENDER, COMPOSITE, etc.  This is essentially a default configuration,
as provided by Gentoo; I didn't really mess around much with what's
being loaded.

Thanks for any help,

Randall Nortman