https://bugs.freedesktop.org/show_bug.cgi?id=106671

--- Comment #25 from Michel Dänzer michel@daenzer.net --- (In reply to Alan W. Irwin from comment #24)

Just now the direct X server failed with a segfault (see the attached log file for the details).

Looks like a Mesa bug. Please install the libgl1-mesa-dri-dbgsym package and attach another log file if it happens again.