After upgrading to Ubuntu 12.04 and restarting my machine, it now won't progress past this:

EXT4-fs (xvda): mounted filesystem with ordered data mode. Opts: (null)
VFS: Mounted root (ext4 filesystem) readonly on device 202:0.
Freeing unused kernel memory: 672k freed
Write protecting the kernel read-only data: 12288k
Freeing unused kernel memory: 1604k freed
Freeing unused kernel memory: 1172k freed

The graphs show that the CPU is spinning at 100% at this point, but I have no idea what it's doing.

I can't boot into the default runlevel or single user mode, but I can boot into /bin/bash and rescue mode.

My /dev/xvda is ext4 and I've tried fscking it, but it hasn't improved the situation. I've tried running with different kernels, including 3.2.1-x86_64-linode23 and the latest 3.0 provided by Linode.

Obviously 12.04 hasn't been released yet so I'm in fairly dangerous territory, but if anyone has any pointers as to how I could progress with debugging this, it would be much appreciated!

Looks like I've run into this problem: https://bugs.launchpad.net/ubuntu/+sour ... bug/942907

Thanks for the report miknight. I was thinking of upgrading to 12.04 as well. Did you try the newer kernel already ?

Yeah I've tried all the kernels, including 3.2.1-x86_64-linode23. I've been trying to get pv_grub working in the hopes of getting more info, but so far it hasn't been working for me.

I've run into the same issue. Anyone find a working setup for this?