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Subject[PATCH 1/8] badpage: simplify page_alloc flag check+clear
Simplify the PAGE_FLAGS checking and clearing when freeing and allocating
a page: check the same flags as before when freeing, clear ALL the flags
(unless PageReserved) when freeing, check ALL flags off when allocating.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---
include/linux/page-flags.h | 25 ++++++++-----------------
mm/page_alloc.c | 19 ++++++-------------
2 files changed, 14 insertions(+), 30 deletions(-)
--- badpage0/include/linux/page-flags.h 2008-11-26 12:18:59.000000000 +0000
+++ badpage1/include/linux/page-flags.h 2008-11-28 20:40:33.000000000 +0000
@@ -375,31 +375,22 @@ static inline void __ClearPageTail(struc
#define __PG_MLOCKED 0
#endif

-#define PAGE_FLAGS (1 << PG_lru | 1 << PG_private | 1 << PG_locked | \
- 1 << PG_buddy | 1 << PG_writeback | \
- 1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
- __PG_UNEVICTABLE | __PG_MLOCKED)
-
-/*
- * Flags checked in bad_page(). Pages on the free list should not have
- * these flags set. It they are, there is a problem.
- */
-#define PAGE_FLAGS_CLEAR_WHEN_BAD (PAGE_FLAGS | \
- 1 << PG_reclaim | 1 << PG_dirty | 1 << PG_swapbacked)
-
/*
* Flags checked when a page is freed. Pages being freed should not have
* these flags set. It they are, there is a problem.
*/
-#define PAGE_FLAGS_CHECK_AT_FREE (PAGE_FLAGS | 1 << PG_reserved)
+#define PAGE_FLAGS_CHECK_AT_FREE \
+ (1 << PG_lru | 1 << PG_private | 1 << PG_locked | \
+ 1 << PG_buddy | 1 << PG_writeback | 1 << PG_reserved | \
+ 1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
+ __PG_UNEVICTABLE | __PG_MLOCKED)

/*
* Flags checked when a page is prepped for return by the page allocator.
- * Pages being prepped should not have these flags set. It they are, there
- * is a problem.
+ * Pages being prepped should not have any flags set. It they are set,
+ * there has been a kernel bug or struct page corruption.
*/
-#define PAGE_FLAGS_CHECK_AT_PREP (PAGE_FLAGS | \
- 1 << PG_reserved | 1 << PG_dirty | 1 << PG_swapbacked)
+#define PAGE_FLAGS_CHECK_AT_PREP ((1 << NR_PAGEFLAGS) - 1)

#endif /* !__GENERATING_BOUNDS_H */
#endif /* PAGE_FLAGS_H */
--- badpage0/mm/page_alloc.c 2008-11-26 12:19:00.000000000 +0000
+++ badpage1/mm/page_alloc.c 2008-11-28 20:40:33.000000000 +0000
@@ -231,7 +231,6 @@ static void bad_page(struct page *page)
printk(KERN_EMERG "Trying to fix it up, but a reboot is needed\n"
KERN_EMERG "Backtrace:\n");
dump_stack();
- page->flags &= ~PAGE_FLAGS_CLEAR_WHEN_BAD;
set_page_count(page, 0);
reset_page_mapcount(page);
page->mapping = NULL;
@@ -468,16 +467,16 @@ static inline int free_pages_check(struc
(page_count(page) != 0) |
(page->flags & PAGE_FLAGS_CHECK_AT_FREE)))
bad_page(page);
- if (PageDirty(page))
- __ClearPageDirty(page);
- if (PageSwapBacked(page))
- __ClearPageSwapBacked(page);
/*
* For now, we report if PG_reserved was found set, but do not
* clear it, and do not free the page. But we shall soon need
* to do more, for when the ZERO_PAGE count wraps negative.
*/
- return PageReserved(page);
+ if (PageReserved(page))
+ return 1;
+ if (page->flags & PAGE_FLAGS_CHECK_AT_PREP)
+ page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+ return 0;
}

/*
@@ -621,13 +620,7 @@ static int prep_new_page(struct page *pa
if (PageReserved(page))
return 1;

- page->flags &= ~(1 << PG_uptodate | 1 << PG_error | 1 << PG_reclaim |
- 1 << PG_referenced | 1 << PG_arch_1 |
- 1 << PG_owner_priv_1 | 1 << PG_mappedtodisk
-#ifdef CONFIG_UNEVICTABLE_LRU
- | 1 << PG_mlocked
-#endif
- );
+ page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
set_page_private(page, 0);
set_page_refcounted(page);


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