From: MAEDA Naoaki <maeda.naoaki@jp.fujitsu.com>

I am testing PCI hot-plug in 2.6.2 kernel, but sometimes a struct resource
tree in kernel/resource.c was broken if multiple hot-plug requests are
issued at the same time.

The reason is lots of drivers call release_region() on hot removal, and
__release_region(), which is invoked by release_region() macro, changes the
tree without holding a writer lock for resource_lock.

I think __release_region() must hold a writer lock as well as
__request_region() does.

A following patch fixes the issue in my environment.