[PATCH 2/2] powerpc - Make the irq reverse mapping radix tree lockless

[Benjamin Herrenschmidt]

BTW. It would be good to try to turn the GFP_ATOMIC into GFP_KERNEL,
maybe using a semaphore instead of a lock to protect insertion vs.
initialisation. The old scheme was fine because if the atomic allocation
failed, it could fallback to the linear search and try again on the next
interrupt. Not anymore.

Ben.