mm/vmalloc.c: use seq_open_private() instead of seq_open()

Using seq_open_private() removes boilerplate code from vmalloc_open().

The resultant code is shorter and easier to follow.

However, please note that seq_open_private() call kzalloc() rather than
kmalloc() which may affect timing due to the memory initialisation
overhead.
Signed-off-by: NRob Jones <rob.jones@codethink.co.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -2646,21 +2646,11 @@ static const struct seq_operations vmalloc_op = {
 
 static int vmalloc_open(struct inode *inode, struct file *file)
 {
-	unsigned int *ptr = NULL;
-	int ret;
-
-	if (IS_ENABLED(CONFIG_NUMA)) {
-		ptr = kmalloc(nr_node_ids * sizeof(unsigned int), GFP_KERNEL);
-		if (ptr == NULL)
-			return -ENOMEM;
-	}
-	ret = seq_open(file, &vmalloc_op);
-	if (!ret) {
-		struct seq_file *m = file->private_data;
-		m->private = ptr;
-	} else
-		kfree(ptr);
-	return ret;
+	if (IS_ENABLED(CONFIG_NUMA))
+		return seq_open_private(file, &vmalloc_op,
+					nr_node_ids * sizeof(unsigned int));
+	else
+		return seq_open(file, &vmalloc_op);
 }
 
 static const struct file_operations proc_vmalloc_operations = {