mm/memory_hotplug.c: check for missing sections in test_pages_in_a_zone()

test_pages_in_a_zone() does not account for the possibility of missing
sections in the given pfn range.  pfn_valid_within always returns 1 when
CONFIG_HOLES_IN_ZONE is not set, allowing invalid pfns from missing
sections to pass the test, leading to a kernel oops.

Wrap an additional pfn loop with PAGES_PER_SECTION granularity to check
for missing sections before proceeding into the zone-check code.

This also prevents a crash from offlining memory devices with missing
sections.  Despite this, it may be a good idea to keep the related patch
'[PATCH 3/3] drivers: memory: prohibit offlining of memory blocks with
missing sections' because missing sections in a memory block may lead to
other problems not covered by the scope of this fix.

Signed-off-by: Andrew Banman <abanman@sgi.com>
Acked-by: Alex Thorlton <athorlton@sgi.com>
Cc: Russ Anderson <rja@sgi.com>
Cc: Alex Thorlton <athorlton@sgi.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Greg KH <greg@kroah.com>
Cc: Seth Jennings <sjennings@variantweb.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 67d488ab495e57b9018484932e135078c787903c..a042a9d537bb31984d6b2a8d3cc8ae1e54361e4f 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1375,23 +1375,30 @@ int is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
  */
 int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
 {
-       unsigned long pfn;
+       unsigned long pfn, sec_end_pfn;
        struct zone *zone = NULL;
        struct page *page;
        int i;
-       for (pfn = start_pfn;
+       for (pfn = start_pfn, sec_end_pfn = SECTION_ALIGN_UP(start_pfn);
             pfn < end_pfn;
-            pfn += MAX_ORDER_NR_PAGES) {
-               i = 0;
-               /* This is just a CONFIG_HOLES_IN_ZONE check.*/
-               while ((i < MAX_ORDER_NR_PAGES) && !pfn_valid_within(pfn + i))
-                       i++;
-               if (i == MAX_ORDER_NR_PAGES)
+            pfn = sec_end_pfn + 1, sec_end_pfn += PAGES_PER_SECTION) {
+               /* Make sure the memory section is present first */
+               if (!present_section_nr(pfn_to_section_nr(pfn)))
                        continue;
-               page = pfn_to_page(pfn + i);
-               if (zone && page_zone(page) != zone)
-                       return 0;
-               zone = page_zone(page);
+               for (; pfn < sec_end_pfn && pfn < end_pfn;
+                    pfn += MAX_ORDER_NR_PAGES) {
+                       i = 0;
+                       /* This is just a CONFIG_HOLES_IN_ZONE check.*/
+                       while ((i < MAX_ORDER_NR_PAGES) &&
+                               !pfn_valid_within(pfn + i))
+                               i++;
+                       if (i == MAX_ORDER_NR_PAGES)
+                               continue;
+                       page = pfn_to_page(pfn + i);
+                       if (zone && page_zone(page) != zone)
+                               return 0;
+                       zone = page_zone(page);
+               }
        }
        return 1;
 }