linux-kernel - [PATCH 3.2 36/70] mm/memory_hotplug.c: check for missing sections in test_pages_in_a

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Message-ID: <lsq.1453087115.844007765@decadent.org.uk>
Date:	Mon, 18 Jan 2016 03:18:35 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Yinghai Lu" <yinghai@...nel.org>,
	"Alex Thorlton" <athorlton@....com>,
	"Seth Jennings" <sjennings@...iantweb.net>,
	"Russ Anderson" <rja@....com>, "Greg KH" <greg@...ah.com>,
	"Andrew Banman" <abanman@....com>
Subject: [PATCH 3.2 36/70] mm/memory_hotplug.c: check for missing sections
 in test_pages_in_a_zone()

3.2.76-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Banman <abanman@....com>

commit 5f0f2887f4de9508dcf438deab28f1de8070c271 upstream.

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@....com>
Acked-by: Alex Thorlton <athorlton@....com>
Cc: Russ Anderson <rja@....com>
Cc: Alex Thorlton <athorlton@....com>
Cc: Yinghai Lu <yinghai@...nel.org>
Cc: Greg KH <greg@...ah.com>
Cc: Seth Jennings <sjennings@...iantweb.net>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/memory_hotplug.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -716,23 +716,30 @@ int is_mem_section_removable(unsigned lo
  */
 static 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;
 }