trace_stack: Fix seqfile memory leak

Every time we cat stack_trace, we leak memory allocated by seq_open().
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A67D8E8.3020500@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_stack.c

@@ -301,17 +301,14 @@ static const struct seq_operations stack_trace_seq_ops = {
 
 static int stack_trace_open(struct inode *inode, struct file *file)
 {
-	int ret;
-
-	ret = seq_open(file, &stack_trace_seq_ops);
-
-	return ret;
+	return seq_open(file, &stack_trace_seq_ops);
 }
 
 static const struct file_operations stack_trace_fops = {
 	.open		= stack_trace_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
+	.release	= seq_release,
 };
 
 int