The previously noted upgrade-to-4.4 recipe:

yum update yum sqlite python-sqlite ; yum update

worked more consistently than running "yum upgrade," but it too fell victim to the futex hang.

In my limited testing, a reboot of the machine before starting the upgrade gave me a 100% success rate.

Given two identical machines, one that had been used for a few days and one that was freshly rebooted, the former would exhibit a futex hang, while the latter updated just fine.

Cheers, Zube