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

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Date:	Wed, 15 Oct 2014 12:20:05 -0700
From:	Yu Zhao <yuzhao@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Hugh Dickins <hughd@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Bob Liu <lliubbo@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	David Rientjes <rientjes@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH v2 2/2] 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.

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Yu Zhao <yuzhao@...gle.com>
---
 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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