[patch 10/22] Fix buddy list race that could lead to page lru list corruptions
From: Greg KH
Date: Thu Apr 13 2006 - 19:10:37 EST
-stable review patch. If anyone has any objections, please let us know.
------------------
From: Nick Piggin <piggin@xxxxxxxxxxxxxxx>
[PATCH] Fix buddy list race that could lead to page lru list corruptions
Rohit found an obscure bug causing buddy list corruption.
page_is_buddy is using a non-atomic test (PagePrivate && page_count == 0)
to determine whether or not a free page's buddy is itself free and in the
buddy lists.
Each of the conjuncts may be true at different times due to unrelated
conditions, so the non-atomic page_is_buddy test may find each conjunct to
be true even if they were not both true at the same time (ie. the page was
not on the buddy lists).
Signed-off-by: Martin Bligh <mbligh@xxxxxxxxxx>
Signed-off-by: Rohit Seth <rohitseth@xxxxxxxxxx>
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
include/linux/mm.h | 5 ++---
include/linux/page-flags.h | 8 +++++++-
mm/page_alloc.c | 31 ++++++++++++++++++-------------
3 files changed, 27 insertions(+), 17 deletions(-)
--- linux-2.6.16.5.orig/include/linux/mm.h
+++ linux-2.6.16.5/include/linux/mm.h
@@ -229,10 +229,9 @@ struct page {
unsigned long private; /* Mapping-private opaque data:
* usually used for buffer_heads
* if PagePrivate set; used for
- * swp_entry_t if PageSwapCache.
- * When page is free, this
+ * swp_entry_t if PageSwapCache;
* indicates order in the buddy
- * system.
+ * system if PG_buddy is set.
*/
struct address_space *mapping; /* If low bit clear, points to
* inode address_space, or NULL.
--- linux-2.6.16.5.orig/include/linux/page-flags.h
+++ linux-2.6.16.5/include/linux/page-flags.h
@@ -74,7 +74,9 @@
#define PG_mappedtodisk 16 /* Has blocks allocated on-disk */
#define PG_reclaim 17 /* To be reclaimed asap */
#define PG_nosave_free 18 /* Free, should not be written */
-#define PG_uncached 19 /* Page has been mapped as uncached */
+#define PG_buddy 19 /* Page is free, on buddy lists */
+
+#define PG_uncached 20 /* Page has been mapped as uncached */
/*
* Global page accounting. One instance per CPU. Only unsigned longs are
@@ -319,6 +321,10 @@ extern void __mod_page_state_offset(unsi
#define SetPageNosaveFree(page) set_bit(PG_nosave_free, &(page)->flags)
#define ClearPageNosaveFree(page) clear_bit(PG_nosave_free, &(page)->flags)
+#define PageBuddy(page) test_bit(PG_buddy, &(page)->flags)
+#define __SetPageBuddy(page) __set_bit(PG_buddy, &(page)->flags)
+#define __ClearPageBuddy(page) __clear_bit(PG_buddy, &(page)->flags)
+
#define PageMappedToDisk(page) test_bit(PG_mappedtodisk, &(page)->flags)
#define SetPageMappedToDisk(page) set_bit(PG_mappedtodisk, &(page)->flags)
#define ClearPageMappedToDisk(page) clear_bit(PG_mappedtodisk, &(page)->flags)
--- linux-2.6.16.5.orig/mm/page_alloc.c
+++ linux-2.6.16.5/mm/page_alloc.c
@@ -153,7 +153,8 @@ static void bad_page(struct page *page)
1 << PG_reclaim |
1 << PG_slab |
1 << PG_swapcache |
- 1 << PG_writeback );
+ 1 << PG_writeback |
+ 1 << PG_buddy );
set_page_count(page, 0);
reset_page_mapcount(page);
page->mapping = NULL;
@@ -224,12 +225,12 @@ static inline unsigned long page_order(s
static inline void set_page_order(struct page *page, int order) {
set_page_private(page, order);
- __SetPagePrivate(page);
+ __SetPageBuddy(page);
}
static inline void rmv_page_order(struct page *page)
{
- __ClearPagePrivate(page);
+ __ClearPageBuddy(page);
set_page_private(page, 0);
}
@@ -268,11 +269,13 @@ __find_combined_index(unsigned long page
* This function checks whether a page is free && is the buddy
* we can do coalesce a page and its buddy if
* (a) the buddy is not in a hole &&
- * (b) the buddy is free &&
- * (c) the buddy is on the buddy system &&
- * (d) a page and its buddy have the same order.
- * for recording page's order, we use page_private(page) and PG_private.
+ * (b) the buddy is in the buddy system &&
+ * (c) a page and its buddy have the same order.
+ *
+ * For recording whether a page is in the buddy system, we use PG_buddy.
+ * Setting, clearing, and testing PG_buddy is serialized by zone->lock.
*
+ * For recording page's order, we use page_private(page).
*/
static inline int page_is_buddy(struct page *page, int order)
{
@@ -281,10 +284,10 @@ static inline int page_is_buddy(struct p
return 0;
#endif
- if (PagePrivate(page) &&
- (page_order(page) == order) &&
- page_count(page) == 0)
+ if (PageBuddy(page) && page_order(page) == order) {
+ BUG_ON(page_count(page) != 0);
return 1;
+ }
return 0;
}
@@ -301,7 +304,7 @@ static inline int page_is_buddy(struct p
* as necessary, plus some accounting needed to play nicely with other
* parts of the VM system.
* At each level, we keep a list of pages, which are heads of continuous
- * free pages of length of (1 << order) and marked with PG_Private.Page's
+ * free pages of length of (1 << order) and marked with PG_buddy. Page's
* order is recorded in page_private(page) field.
* So when we are allocating or freeing one, we can derive the state of the
* other. That is, if we allocate a small block, and both were
@@ -364,7 +367,8 @@ static inline int free_pages_check(struc
1 << PG_slab |
1 << PG_swapcache |
1 << PG_writeback |
- 1 << PG_reserved ))))
+ 1 << PG_reserved |
+ 1 << PG_buddy ))))
bad_page(page);
if (PageDirty(page))
__ClearPageDirty(page);
@@ -522,7 +526,8 @@ static int prep_new_page(struct page *pa
1 << PG_slab |
1 << PG_swapcache |
1 << PG_writeback |
- 1 << PG_reserved ))))
+ 1 << PG_reserved |
+ 1 << PG_buddy ))))
bad_page(page);
/*
--
-
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