this applies for nvidia-drivers: xorg.log: [ 4.091] (EE) NVIDIA(0): Failed to initialize the GLX module; please check in your X [ 4.091] (EE) NVIDIA(0): log file that the GLX module has been loaded in your X [ 4.091] (EE) NVIDIA(0): server, and that the module is the NVIDIA GLX module. If [ 4.091] (EE) NVIDIA(0): you continue to encounter problems, Please try [ 4.091] (EE) NVIDIA(0): reinstalling the NVIDIA driver. masking the following packages is a workaround: /etc/portage/package.mask: =app-admin/eselect-opengl-1.3.1-r1 =media-libs/mesa-10.3.5-r1 =x11-base/xorg-server-1.16.2.901-r1 =x11-proto/glproto-1.4.17-r1 =app-emulation/emul-linux-x86-opengl-20140508-r1 I had to mask all 5 of them to avoid block-conflicts. For me, the original update also changed eselect opengl from nvidia to xorg-x11, so after downgrading, I had to change this setting as well.
*** This bug has been marked as a duplicate of bug 534128 ***
