[PATCH] [12/16] HWPOISON: check and isolate corrupted free pages

[Andi Kleen <andi@firstfloor.org>]

From: Wu Fengguang <fengguang.wu@intel.com>

If memory corruption hits the free buddy pages, we can safely ignore them.
No one will access them until page allocation time, then prep_new_page()
will automatically check and isolate PG_hwpoison page for us (for 0-order
allocation).

This patch expands prep_new_page() to check every component page in a high
order page allocation, in order to completely stop PG_hwpoison pages from
being recirculated.

Note that the common case -- only allocating a single page, doesn't
do any more work than before. Allocating > order 0 does a bit more work,
but that's relatively uncommon.

This simple implementation may drop some innocent neighbor pages, hopefully
it is not a big problem because the event should be rare enough.

This patch adds some runtime costs to high order page users.

[AK: Improved description]
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
 mm/page_alloc.c |   22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

Index: linux/mm/page_alloc.c
===================================================================
--- linux.orig/mm/page_alloc.c	2009-05-29 23:32:08.000000000 +0200
+++ linux/mm/page_alloc.c	2009-05-29 23:32:11.000000000 +0200
@@ -633,12 +633,22 @@
  */
 static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
 {
-	if (unlikely(page_mapcount(page) |
-		(page->mapping != NULL)  |
-		(page_count(page) != 0)  |
-		(page->flags & PAGE_FLAGS_CHECK_AT_PREP))) {
-		bad_page(page);
-		return 1;
+	int i;
+
+	for (i = 0; i < (1 << order); i++) {
+		struct page *p = page + i;
+
+		if (unlikely(page_mapcount(p) |
+			(p->mapping != NULL)  |
+			(page_count(p) != 0)  |
+			(p->flags & PAGE_FLAGS_CHECK_AT_PREP))) {
+			/*
+			 * The whole array of pages will be dropped,
+			 * hopefully this is a rare and abnormal event.
+			 */
+			bad_page(p);
+			return 1;
+		}
 	}
 
 	set_page_private(page, 0);

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