mm/sparse.c: check the return value of sparse_index_alloc()

Since sparse_index_alloc() can return NULL on memory allocation failure,
we must deal with the failure condition when calling it.
Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/sparse.c

@@ -83,6 +83,8 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid)
 		return -EEXIST;
 
 	section = sparse_index_alloc(nid);
+	if (!section)
+		return -ENOMEM;
 	/*
 	 * This lock keeps two different sections from
 	 * reallocating for the same index