Patch "mm/memory_hotplug.c: check start_pfn in test_pages_in_a_zone()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

mm/memory_hotplug.c: check start_pfn in test_pages_in_a_zone()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-memory_hotplug.c-check-start_pfn-in-test_pages_in_a_zone.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Toshi Kani <[email protected]>
Date: Fri, 3 Feb 2017 13:13:20 -0800
Subject: mm/memory_hotplug.c: check start_pfn in test_pages_in_a_zone()

From: Toshi Kani <[email protected]>

commit deb88a2a19e85842d79ba96b05031739ec327ff4 upstream.

Patch series "fix a kernel oops when reading sysfs valid_zones", v2.

A sysfs memory file is created for each 2GiB memory block on x86-64 when the system has 64GiB or more memory. [1] When the start address of a memory block is not backed by struct page, i.e. a memory range is not aligned by 2GiB, reading its 'valid_zones' attribute file leads to a kernel oops. This issue was observed on multiple x86-64 systems with more than 64GiB of memory. This patch-set fixes this issue.

Patch 1 first fixes an issue in test_pages_in_a_zone(), which does not test the start section.

Patch 2 then fixes the kernel oops by extending test_pages_in_a_zone() to return valid [start, end).

Note for stable kernels: The memory block size change was made by commit bdee237c0343 ("x86: mm: Use 2GB memory block size on large-memory x86-64 systems"), which was accepted to 3.9. However, this patch-set depends on (and fixes) the change to test_pages_in_a_zone() made by commit 5f0f2887f4de ("mm/memory_hotplug.c: check for missing sections in test_pages_in_a_zone()"), which was accepted to 4.4.

So, I recommend that we backport it up to 4.4.

[1] 'Commit bdee237c0343 ("x86: mm: Use 2GB memory block size on

    large-memory x86-64 systems")'

This patch (of 2):

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.

---
 mm/memory_hotplug.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

@@ -1483,7 +1483,7 @@ bool is_mem_section_removable(unsigned l
 }
 
 /*
- * 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)
 {

@@ -1491,9 +1491,9 @@ int test_pages_in_a_zone(unsigned long s
 	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;

@@ -1512,7 +1512,11 @@ int test_pages_in_a_zone(unsigned long s
 			zone = page_zone(page);
 		}
 	}
-	return 1;
+
+	if (zone)
+		return 1;
+	else
+		return 0;
 }
 
 /*

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mm-memory_hotplug.c-check-start_pfn-in-test_pages_in_a_zone.patch queue-4.9/base-memory-hotplug-fix-a-kernel-oops-in-show_valid_zones.patch