Fix __pfn_to_page(pfn) for CONFIG_DISCONTIGMEM=y

Fix the __pfn_to_page(pfn) macro so that it doesn't evaluate its
argument twice in the CONFIG_DISCONTIGMEM=y case, because 'pfn' may
be a result of a funtion call having side effects.

For example, the hibernation code applies pfn_to_page(pfn) to the
result of a function returning the pfn corresponding to the next set
bit in a bitmap and the current bit position is modified on each
call.  This leads to "interesting" failures for CONFIG_DISCONTIGMEM=y
due to the current behavior of __pfn_to_page(pfn).
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-generic/memory_model.h

@@ -34,7 +34,7 @@
 
 #define __pfn_to_page(pfn)			\
 ({	unsigned long __pfn = (pfn);		\
-	unsigned long __nid = arch_pfn_to_nid(pfn);  \
+	unsigned long __nid = arch_pfn_to_nid(__pfn);  \
 	NODE_DATA(__nid)->node_mem_map + arch_local_page_offset(__pfn, __nid);\
 })