Revert "mm: Check if section present during memory block (un)registering"

This reverts commit 7568fb63f57ac8672f8bf2018171255441238882 as it's
already in Linus's tree through a different patch.

Reported-by: Tony Luck <[e-mail]>
Cc: Yinghai Lu <[e-mail]>
Cc: [e-mail] #v3.15
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/node.c

···
 	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
 	sect_end_pfn += PAGES_PER_SECTION - 1;
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
-		int page_nid, scn_nr;
-
-		/*
-		 * memory block could have several absent sections from start.
-		 * skip pfn range from absent section
-		 */
-		scn_nr = pfn_to_section_nr(pfn);
-		if (!present_section_nr(scn_nr)) {
-			pfn = round_down(pfn + PAGES_PER_SECTION,
-					 PAGES_PER_SECTION) - 1;
-			continue;
-		}
+		int page_nid;
 
 		/*
 		 * memory block could have several absent sections from start.
···
 		return -ENOMEM;
 	nodes_clear(*unlinked_nodes);
 
-	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
-	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
-	sect_end_pfn += PAGES_PER_SECTION - 1;
+	sect_start_pfn = section_nr_to_pfn(phys_index);
+	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
-		int nid, scn_nr;
-
-		/*
-		 * memory block could have several absent sections from start.
-		 * skip pfn range from absent section
-		 */
-		scn_nr = pfn_to_section_nr(pfn);
-		if (!present_section_nr(scn_nr)) {
-			pfn = round_down(pfn + PAGES_PER_SECTION,
-					 PAGES_PER_SECTION) - 1;
-			continue;
-		}
+		int nid;
 
 		nid = get_nid_for_pfn(pfn);
 		if (nid < 0)