mm/sparse: guard the size of mem_section is power of 2

We usually have this check, while commit 2a3cb8b ("mm/sparse: delete
old sparse_init and enable new one") missed to take it.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Wei Yang <[email protected]>
Acked-by: Oscar Salvador <[email protected]>
Reviewed-by: Pasha Tatashin <[email protected]>
Cc: "Mike Rapoport (IBM)" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: RichardWeiYang

mm/sparse.c

@@ -560,6 +560,8 @@ void __init sparse_init(void)
 	unsigned long pnum_end, pnum_begin, map_count = 1;
 	int nid_begin;
 
+	/* see include/linux/mmzone.h 'struct mem_section' definition */
+	BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
 	memblocks_present();
 
 	pnum_begin = first_present_section_nr();