[hardy] X locks with lots of "tossed event which came in late. mieqEnequeue: out-of-order valuator event; dropping."

Binary package hint: xserver-xorg-core

I'm running the latest Hardy as of the reporting date on an HP desktop with Pentium D, 3 GB RAM, ATI Radeon X600 (PCIE) (RV380) video card.

Since about one week, I'm experiencing consistent locks of X after a seemingly random time after login. After a recent batch of updates which included xserver-xorg-core 2:1.4.1~git20080105-1ubuntu3 and, if memory serves well, no other obvious culprit, the problem got worse, in that the lock now consistently happens within minutes of boot, often even while the gnome desktop is still loading after login.

When the lock happens, X uses up 98-100% processor time, keyboard and mouse are unresponsive, and I cannot even do CTRL-ALT-BACKSPACE, CTRL-ALT-CANC or any of the SysReq combinations, while Xorg.0.log gets filled with these messages:

tossed event which came in late
mieqEnequeue: out-of-order valuator event; dropping.

I can ssh into the box to inspect things, but nothing I've tried (restarting gdm, killing compiz, killing X) managed to restore the system.

These symptoms look somewhat like those described in bug #175744 against Compiz, and especially bug #173653, which was marked as a dupe of the former. Anyway, after a few attempts failed because the lock happened before I could get to the appearence preferences, I finally managed to disable Compiz, just to find that the lock still happens with Compiz disabled (I even used ps aux | grep compiz to confirm that Compiz was not running, and indeed it was not).

I'm not sure what kind of information might be needed, so I'm attaching Xorg.0.log from the frozen machine, as well as the output of sudo lspci -vv. Please, let me know if you need further input, and just ask me if you need to run some test or anything else.