[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@google.com>
Signed-off-by: Rohit Seth <rohitseth@google.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6aa016f..1154684 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -229,10 +229,9 @@
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.
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 9ea629c..547aac7 100644
--- a/include/linux/page-flags.h
+++ b/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
@@ -317,6 +319,10 @@
#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)