[PATCH] SPARSEMEM incorrectly calculates section number

A bad calculation/loop in __section_nr() could result in incorrect section
information being put into sysfs memory entries.  This primarily impacts
memory add operations as the sysfs information is used while onlining new
memory.

Fix suggested by Dave Hansen.

Note that the bug may not be obvious from the patch.  It actually occurs in
the function's return statement:

	return (root_nr * SECTIONS_PER_ROOT) + (ms - root);

In the existing code, root_nr has already been multiplied by
SECTIONS_PER_ROOT.
Signed-off-by: Mike Kravetz <kravetz@us.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/sparse.c

@@ -87,11 +87,8 @@ int __section_nr(struct mem_section* ms)
 	unsigned long root_nr;
 	struct mem_section* root;
 
-	for (root_nr = 0;
-	     root_nr < NR_MEM_SECTIONS;
-	     root_nr += SECTIONS_PER_ROOT) {
-		root = __nr_to_section(root_nr);
-
+	for (root_nr = 0; root_nr < NR_SECTION_ROOTS; root_nr++) {
+		root = __nr_to_section(root_nr * SECTIONS_PER_ROOT);
 		if (!root)
 			continue;