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Subject[PATCH 2/8] badpage: keep any bad page out of circulation
Until now the bad_page() checkers have special-cased PageReserved, keeping
those pages out of circulation thereafter. Now extend the special case to
all: we want to keep ANY page with bad state out of circulation - the
"free" page may well be in use by something.

Leave the bad state of those pages untouched, for examination by debuggers;
except for PageBuddy - leaving that set would risk bringing the page back.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---
mm/page_alloc.c | 52 +++++++++++++++++++++-------------------------
1 file changed, 24 insertions(+), 28 deletions(-)
--- badpage1/mm/page_alloc.c 2008-11-28 20:40:33.000000000 +0000
+++ badpage2/mm/page_alloc.c 2008-11-28 20:40:36.000000000 +0000
@@ -231,9 +231,9 @@ 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();
- set_page_count(page, 0);
- reset_page_mapcount(page);
- page->mapping = NULL;
+
+ /* Leave bad fields for debug, except PageBuddy could make trouble */
+ __ClearPageBuddy(page);
add_taint(TAINT_BAD_PAGE);
}

@@ -290,25 +290,31 @@ void prep_compound_gigantic_page(struct
}
#endif

-static void destroy_compound_page(struct page *page, unsigned long order)
+static int destroy_compound_page(struct page *page, unsigned long order)
{
int i;
int nr_pages = 1 << order;
+ int bad = 0;

- if (unlikely(compound_order(page) != order))
+ if (unlikely(compound_order(page) != order) ||
+ unlikely(!PageHead(page))) {
bad_page(page);
+ bad++;
+ }

- if (unlikely(!PageHead(page)))
- bad_page(page);
__ClearPageHead(page);
+
for (i = 1; i < nr_pages; i++) {
struct page *p = page + i;

- if (unlikely(!PageTail(p) |
- (p->first_page != page)))
+ if (unlikely(!PageTail(p) | (p->first_page != page))) {
bad_page(page);
+ bad++;
+ }
__ClearPageTail(p);
}
+
+ return bad;
}

static inline void prep_zero_page(struct page *page, int order, gfp_t gfp_flags)
@@ -428,7 +434,8 @@ static inline void __free_one_page(struc
int migratetype = get_pageblock_migratetype(page);

if (unlikely(PageCompound(page)))
- destroy_compound_page(page, order);
+ if (unlikely(destroy_compound_page(page, order)))
+ return;

page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);

@@ -465,15 +472,10 @@ static inline int free_pages_check(struc
if (unlikely(page_mapcount(page) |
(page->mapping != NULL) |
(page_count(page) != 0) |
- (page->flags & PAGE_FLAGS_CHECK_AT_FREE)))
+ (page->flags & PAGE_FLAGS_CHECK_AT_FREE))) {
bad_page(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.
- */
- if (PageReserved(page))
return 1;
+ }
if (page->flags & PAGE_FLAGS_CHECK_AT_PREP)
page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
return 0;
@@ -521,11 +523,11 @@ static void __free_pages_ok(struct page
{
unsigned long flags;
int i;
- int reserved = 0;
+ int bad = 0;

for (i = 0 ; i < (1 << order) ; ++i)
- reserved += free_pages_check(page + i);
- if (reserved)
+ bad += free_pages_check(page + i);
+ if (bad)
return;

if (!PageHighMem(page)) {
@@ -610,17 +612,11 @@ static int prep_new_page(struct page *pa
if (unlikely(page_mapcount(page) |
(page->mapping != NULL) |
(page_count(page) != 0) |
- (page->flags & PAGE_FLAGS_CHECK_AT_PREP)))
+ (page->flags & PAGE_FLAGS_CHECK_AT_PREP))) {
bad_page(page);
-
- /*
- * For now, we report if PG_reserved was found set, but do not
- * clear it, and do not allocate the page: as a safety net.
- */
- if (PageReserved(page))
return 1;
+ }

- page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
set_page_private(page, 0);
set_page_refcounted(page);


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