[PATCH v2 1/2] mm/memory_hotplug.c: check start_pfn in test_pages_in_a_zone()

[Toshi Kani]

test_pages_in_a_zone() does not check 'start_pfn' when it is
aligned by section since 'sec_end_pfn' is set equal to 'pfn'.
Since this function is called for testing the range of a sysfs
memory file, 'start_pfn' is always aligned by section.

Fix it by properly setting 'sec_end_pfn' to the next section pfn.

Also make sure that this function returns 1 only when the range
belongs to a zone.

Signed-off-by: Toshi Kani <toshi.k...@hpe.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Andrew Banman <aban...@sgi.com>
Cc: Reza Arbab <ar...@linux.vnet.ibm.com>
Cc: <sta...@vger.kernel.org> # v4.4+
---
 mm/memory_hotplug.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 3e3db7a..c845c5f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1489,7 +1489,7 @@ bool is_mem_section_removable(unsigned long start_pfn, 
unsigned long nr_pages)
 }
 
 /*
- * Confirm all pages in a range [start, end) is belongs to the same zone.
+ * Confirm all pages in a range [start, end) belong to the same zone.
  */
 int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
 {
@@ -1497,9 +1497,9 @@ int test_pages_in_a_zone(unsigned long start_pfn, 
unsigned long end_pfn)
        struct zone *zone = NULL;
        struct page *page;
        int i;
-       for (pfn = start_pfn, sec_end_pfn = SECTION_ALIGN_UP(start_pfn);
+       for (pfn = start_pfn, sec_end_pfn = SECTION_ALIGN_UP(start_pfn + 1);
             pfn < end_pfn;
-            pfn = sec_end_pfn + 1, sec_end_pfn += PAGES_PER_SECTION) {
+            pfn = sec_end_pfn, sec_end_pfn += PAGES_PER_SECTION) {
                /* Make sure the memory section is present first */
                if (!present_section_nr(pfn_to_section_nr(pfn)))
                        continue;
@@ -1518,7 +1518,11 @@ int test_pages_in_a_zone(unsigned long start_pfn, 
unsigned long end_pfn)
                        zone = page_zone(page);
                }
        }
-       return 1;
+
+       if (zone)
+               return 1;
+       else
+               return 0;
 }
 
 /*