[PATCH 3.2 180/200] mm/hugetlb: check for pte NULL pointer in __page_check_address()

[Ben Hutchings]

3.2.56-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jianguo Wu <wujianguo@xxxxxxxxxx>

commit 98398c32f6687ee1e1f3ae084effb4b75adb0747 upstream.

In __page_check_address(), if address's pud is not present,
huge_pte_offset() will return NULL, we should check the return value.

Signed-off-by: Jianguo Wu <wujianguo@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: qiuxishi <qiuxishi@xxxxxxxxxx>
Cc: Hanjun Guo <guohanjun@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 mm/rmap.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -581,7 +581,11 @@ pte_t *__page_check_address(struct page
 	spinlock_t *ptl;
 
 	if (unlikely(PageHuge(page))) {
+		/* when pud is not present, pte will be NULL */
 		pte = huge_pte_offset(mm, address);
+		if (!pte)
+			return NULL;
+
 		ptl = &mm->page_table_lock;
 		goto check;
 	}

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