Comment 58 for bug 1039202

There's a known issue with NVC8's whereby there's some unknown deficiency in the nouveau ctxsw firmware causes most of those cards to hang. If the issue goes away when you use blob firmware (see http://nouveau.freedesktop.org/wiki/VideoAcceleration/#firmware for an easy way to get that set up -- you'll also need to add nouveau.config=NvGrUseFW=1 to the kernel cmdline) then you have the same issue as bug 54437.