mm: more checks on free_pages_prepare() for tail pages

Although it was not called, destroy_compound_page() did some potentially
useful checks.  Let's re-introduce them in free_pages_prepare(), where
they can be actually triggered when CONFIG_DEBUG_VM=y.

compound_order() assert is already in free_pages_prepare().  We have few
checks for tail pages left.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 4 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 12d55b859d3f..0081228d1caa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -764,21 +764,40 @@ static void free_one_page(struct zone *zone,
         spin_unlock(&zone->lock);
 }
 
+static int free_tail_pages_check(struct page *head_page, struct page *page)
+{
+        if (!IS_ENABLED(CONFIG_DEBUG_VM))
+                return 0;
+        if (unlikely(!PageTail(page))) {
+                bad_page(page, "PageTail not set", 0);
+                return 1;
+        }
+        if (unlikely(page->first_page != head_page)) {
+                bad_page(page, "first_page not consistent", 0);
+                return 1;
+        }
+        return 0;
+}
+
 static bool free_pages_prepare(struct page *page, unsigned int order)
 {
-        int i;
-        int bad = 0;
+        bool compound = PageCompound(page);
+        int i, bad = 0;
 
         VM_BUG_ON_PAGE(PageTail(page), page);
-        VM_BUG_ON_PAGE(PageHead(page) && compound_order(page) != order, page);
+        VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);
 
         trace_mm_page_free(page, order);
         kmemcheck_free_shadow(page, order);
 
         if (PageAnon(page))
                 page->mapping = NULL;
-        for (i = 0; i < (1 << order); i++)
+        bad += free_pages_check(page);
+        for (i = 1; i < (1 << order); i++) {
+                if (compound)
+                        bad += free_tail_pages_check(page, page + i);
                 bad += free_pages_check(page + i);
+        }
         if (bad)
                 return false;