mm: verify compound order when freeing a page

This allows us to catch the bug fixed in the previous patch (mm: free
compound page with correct order).

Here we also verify whether a page is tail page or not -- tail pages are
supposed to be freed along with their head, not by themselves.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: David Rientjes <rientjes@google.com>
Cc: Bob Liu <lliubbo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f3a6bf12cbc1..b7c18f094697 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -741,6 +741,9 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
         int i;
         int bad = 0;
 
+        VM_BUG_ON_PAGE(PageTail(page), page);
+        VM_BUG_ON_PAGE(PageHead(page) && compound_order(page) != order, page);
+
         trace_mm_page_free(page, order);
         kmemcheck_free_shadow(page, order);