I have the same problem reported by Ludovico and, as noted in the upstream bug report already pointed out by Reinhard [1], reducing the amount of ram from 4G to something smaller (e.g. 3.5G) with the mem=3500M kernel boot parameter causes the bug to disappear and can be used as a temporary workaround. [1] http://bugs.freedesktop.org/show_bug.cgi?id=25510