Since upgrading from a 3.6.10 kernel to a 3.7.9 kernel (Fedora 18), the system
started hanging while loading gdm. Going back to the 3.6 kernel works, going to
a 3.8 kernel hangs the same way.

The hang manifests first as the gdm spinning "loading" cursor stopping,
followed a few seconds later by a screen full of a repeated noise pattern
(different for each boot, but looks like a small block of noise tiled all over
the screen). The machine does not answer to the keyboard (num lock/caps lock
LEDs) or the network (by this point NetworkManager already started the
interface, so I can get a few pings before it hangs).

In particular, it is not the initial modeset when loading the module which
hangs; it is only gdm. If I boot with systemd.unit=multi-user.target, I can
boot without any hangs, load netconsole, and isolate graphical.target to load
gdm to see it hang. I used that to capture the kernel messages until the hang
for the Fedora 3.7.9 kernel.

I also managed to capture the Xorg.0.log for the attempt with the 3.8 kernel
(booting directly into graphical.target).

The relevant version numbers are:

kernel-3.6.10-4.fc18.x86_64 (works)
kernel-3.7.9-201.fc18.x86_64 (hangs)
Upstream 3.8 kernel with a Fedora config (hangs)
xorg-x11-server-Xorg-1.13.2-2.fc18.x86_64
xorg-x11-drv-nouveau-1.0.6-1.fc18.x86_64
libdrm-2.4.42-1.fc18.x86_64
mesa-dri-drivers-9.0.1-4.fc18.x86_64

I also attempted once booting 3.7.9 with nouveau.config=NvPCIE=0 as suggested
at bug #58776; it did not make any visible difference.