kernel stops booting on quad powermac

Oddly, a recent kernel (23fd50450a34f2558070ceabb0bfebc1c9604af5) stops
booting at "windfarm: Drive bay control loop started.", while previously
"windfarm: CPUs control loops started" was displayed a long time, i.e.
Backside took very long to start.

Haven't had a chance to look into it yet, any ideas? I do have NO_HZ
enabled. I wanted to test the irqtrace patch but I doubt it would be
causing this, usually bugs there caused hangs very early, not this late
in the boot sequence.

johannes