Xorg crash prevents login

[fcole90]

After a recent update, it's no more possible to log in to Ubuntu 16.04 trough lightdm with Unity.

I'm attaching .xsession-errors hoping it can be useful.

I'm reporting this from another partition with Trusty, because I did'n know how to report without any GUI. I'm willing to add details if anyone helps me on how to send them from the CLI.

[fcole90 (fcole90)]

I installed an xfce session to report the bug, but I cannot run ubuntu bug:

$ubuntu-bug 1543458
sys:1: PyGIWarning: Wnck was imported without specifying a version first. Use gi.require_version('Wnck', '3.0') before import to ensure that the right version gets loaded.
sys:1: PyGIWarning: GdkX11 was imported without specifying a version first. Use gi.require_version('GdkX11', '3.0') before import to ensure that the right version gets loaded.
Xlib: extension "GLX" missing on display ":0".

(apport-gtk:7836): Gtk-WARNING **: Theme parsing error: gtk-widgets.css:2149:29: Expected a valid selector

[fcole90 (fcole90)]

The "Xlib: extension "GLX" missing on display ":0"" message suggests it's indeed a problem with the GPU. I found that it could be caused by bugs with nvidia drivers. This could be the case, as mine it's an optimus laptop with NVIDIA GTX 850m.

[fcole90 (fcole90)]

This bug is a duplicate of https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1543746