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>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 28 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b90a74d28485..bd330252fc77 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -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 page *page, unsigned long order)
 }
 #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(struct page *page,
         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(struct page *page)
         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 *page, unsigned int order)
 {
         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 *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)))
+                (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);