[PATCH v2 2/2] mm: verify compound order when freeing a page

[Yu Zhao]

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.

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
---
 mm/page_alloc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 736d8e1..5bf44e4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -750,6 +750,9 @@ 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);
 
-- 
2.1.0.rc2.206.gedb03e5

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