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

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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.kani@hpe.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrew Banman <abanman@sgi.com>
Cc: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: <stable@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;
 }
 
 /*

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[PATCH v2 0/2] fix a kernel oops when reading sysfs valid_zones Toshi Kani <toshi.kani@hpe.com> - 2017-01-27 22:40 +0100
  [PATCH v2 2/2] base/memory, hotplug: fix a kernel oops in show_valid_zones() Toshi Kani <toshi.kani@hpe.com> - 2017-01-27 22:40 +0100
  [PATCH v2 1/2] mm/memory_hotplug.c: check start_pfn in test_pages_in_a_zone() Toshi Kani <toshi.kani@hpe.com> - 2017-01-27 22:40 +0100

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