cpu alloc: Add debugging checks

Add some debugging check to CPU_OFFSET.

If a processor is not available then BUG. If a processor is not online
then show a warning. (At some point we need to get to the point where
we only manage per cpu data for online processors.)

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 include/linux/percpu.h |   11 +++++++++++
 1 file changed, 11 insertions(+)

Index: linux-2.6/include/linux/percpu.h
===================================================================
--- linux-2.6.orig/include/linux/percpu.h	2007-11-17 19:24:24.219224991 -0800
+++ linux-2.6/include/linux/percpu.h	2007-11-17 21:04:58.248390176 -0800
@@ -66,8 +66,19 @@ DECLARE_PER_CPU(cpumask_t, cpu_mask);
  * handled from an interrupt context).
  */
 
+#ifdef CONFIG_DEBUG_VM
+#define CPU_OFFSET(__cpu) ({						\
+	BUG_ON(!cpu_isset((__cpu), cpu_possible_map));			\
+	if (system_state == SYSTEM_RUNNING)				\
+		WARN_ON(!cpu_isset((__cpu), cpu_online_map));		\
+	(((unsigned long)(__cpu) <<					\
+			(CONFIG_CPU_AREA_ORDER + PAGE_SHIFT)));		\
+})
+
+#else
 #define CPU_OFFSET(__cpu) \
 	((unsigned long)(__cpu) << (CONFIG_CPU_AREA_ORDER + PAGE_SHIFT))
+#endif
 
 #define CPU_PTR(__p, __cpu) ((__typeof__(__p))((void *)(__p) + \
 							CPU_OFFSET(__cpu)))