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

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Message-Id: <1413317800-25450-2-git-send-email-yuzhao@google.com>
Date:	Tue, 14 Oct 2014 13:16:40 -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,
	Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH 2/2] mm: verify compound order when freeing a page

This allows us to easily catch the bug fixed in previous patch.

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@...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..2bcc770 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(PageTail(page));
+	VM_BUG_ON(PageHead(page) && compound_order(page) != order);
+
 	trace_mm_page_free(page, order);
 	kmemcheck_free_shadow(page, order);
 
-- 
2.1.0.rc2.206.gedb03e5

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