From: Manfred Spraul <manfred@colorfullife.com>

attached is the lockless semop patch. I did another test run with 
idle=poll on an pentium III, and it remained unchanged: 99.9% direct 
fast path, 0.1% race with wakeup against writing the final result code:

http://khack.osdl.org/stp/282936/environment/proc/slabinfo

That means there is no immediate need to add the two-stage
implementation to finish_wait.

It reduces the spinlock operations on the semaphore array spinlock by 1/3.