Most recent kernel where this bug did not occur: not found Distribution: Debian Hardware Environment: Toshiba Tecra S1 Software Environment: Debian sarge / Xorg 6.9.0.dfsg.1-5bpo2 Problem Description: X does not start in about 1 of 7 times. Syslog says [drm] writeback test failed Steps to reproduce: reboot 10 times ....
Created attachment 8675 [details] Trace of two situtation where x hangs on loading X server stops loading with a black screen. It's not possible to switch to text console. Here are two traces of this situation with SysReq-T.
This is an X radeon driver issue that was fixed in the xf86-video-ati releases 6.5.8 (for X.Org 7.0) and 6.6.0 (for X.Org 7.1).
Thank you for that information. Will try that asap.