How to debug X lockup (advice from gurus wanted)

[Roberto Ragusa]

Hi,

it sometimes happens to me that X completely locks up, while the
machine is still alive on the network.

This is on F14, untainted kernel, nouveau driver, no 3D used,
KDE desktop on a 32-bit machine with 8GiB RAM and PAE kernel.
It typically happens when something is going to be drawn on
the screen (a window pops up or virtual desktop change).

I would like to open a bug, but I'm not able to attach any kind
of usable log; dmesg says nothing, all I can say is that
the screen remains frozen (including the pointer), the X
server and the kernel keep doing some "SIG ALRM" stuff and
any attempt to access the X server stalls the command (xrandr
or xset, for example), in a Ctrl-C responsive way.

This is happening on different kernel revisions. This laptop
is perfectly stable and it sometimes takes a few weeks to show
the problem (using suspend during the night).

If I do a fresh reboot there is a high probability of a lockup
in a mater of minutes/hours.
Just as if there were lucky and unlucky reboots (important stuff
being placed in memory areas which is easily corrupted?).

Another data point: this laptop sometimes fails to suspend properly
(remains frozen). In any case the last frozen-X event happened
today before any attempt to suspend, so I can not blame the
BIOS and ACPI parts.

Any idea?

-- 
   Roberto Ragusa    mail at robertoragusa.it