tracing/stat: Fix seqfile memory leak

Every time we cat a trace_stat file, we leak memory allocated by
seq_open().

Also fix memory leak in a failure path in tracing_stat_open().
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A67D92B.4060704@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_stat.c

@@ -73,7 +73,7 @@ static struct rb_node *release_next(struct rb_node *node)
 	}
 }
 
-static void reset_stat_session(struct stat_session *session)
+static void __reset_stat_session(struct stat_session *session)
 {
 	struct rb_node *node = session->stat_root.rb_node;
 
@@ -83,10 +83,17 @@ static void reset_stat_session(struct stat_session *session)
 	session->stat_root = RB_ROOT;
 }
 
+static void reset_stat_session(struct stat_session *session)
+{
+	mutex_lock(&session->stat_mutex);
+	__reset_stat_session(session);
+	mutex_unlock(&session->stat_mutex);
+}
+
 static void destroy_session(struct stat_session *session)
 {
 	debugfs_remove(session->file);
-	reset_stat_session(session);
+	__reset_stat_session(session);
 	mutex_destroy(&session->stat_mutex);
 	kfree(session);
 }
@@ -150,7 +157,7 @@ static int stat_seq_init(struct stat_session *session)
 	int i;
 
 	mutex_lock(&session->stat_mutex);
-	reset_stat_session(session);
+	__reset_stat_session(session);
 
 	if (!ts->stat_cmp)
 		ts->stat_cmp = dummy_cmp;
@@ -183,7 +190,7 @@ exit:
 	return ret;
 
 exit_free_rbtree:
-	reset_stat_session(session);
+	__reset_stat_session(session);
 	mutex_unlock(&session->stat_mutex);
 	return ret;
 }
@@ -250,16 +257,21 @@ static const struct seq_operations trace_stat_seq_ops = {
 static int tracing_stat_open(struct inode *inode, struct file *file)
 {
 	int ret;
-
+	struct seq_file *m;
 	struct stat_session *session = inode->i_private;
 
+	ret = stat_seq_init(session);
+	if (ret)
+		return ret;
+
 	ret = seq_open(file, &trace_stat_seq_ops);
-	if (!ret) {
-		struct seq_file *m = file->private_data;
-		m->private = session;
-		ret = stat_seq_init(session);
+	if (ret) {
+		reset_stat_session(session);
+		return ret;
 	}
 
+	m = file->private_data;
+	m->private = session;
 	return ret;
 }
 
@@ -270,11 +282,9 @@ static int tracing_stat_release(struct inode *i, struct file *f)
 {
 	struct stat_session *session = i->i_private;
 
-	mutex_lock(&session->stat_mutex);
 	reset_stat_session(session);
-	mutex_unlock(&session->stat_mutex);
 
-	return 0;
+	return seq_release(i, f);
 }
 
 static const struct file_operations tracing_stat_fops = {