Comment 9 for bug 1124576

This is the likely fix:

commit 56fd91fc830d7a210e3a0e70ab41261a1f5baa83
Author: Chris Wilson <email address hidden>
Date: Mon Feb 25 15:18:46 2013 +0000

    sna/gen3+: Restart vertex space checks after lock contention

    If we end up contending for the vertex lock, we need to double check
    there is sufficient vertex space left for us.

    Bugzilla: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1124576