I have been running some tests on a fc14 instance on rackspace. I can reliably produce a hang in the spinlock test by repeatedly running 'test spinlock' from a 'test' binary built in release mode. It seemed easier to produce this hang with a v8 build than with a sm build but both build types were subject to the hang.

My build on that machine seemed to use the __USE_XOPEN2K variety of spinlock.