Comment 57 for bug 574910

Al, just before you posted about your lock-up, an instance of mine (not running one of these test kernels) was experiencing some difficulty in a US-EAST-1 availability zone, I think related to EBS, it had trouble accepting connections and running new processes for about 15 minutes and was magically resolved (usually coincides with AWS posting about EBS issues on their status feed but my problems happened after yesterday's reported EBS issues).
Perhaps you could try again to rule out AWS issues?