tracing: Do not assign filp->private_data to freed memory

In system_tr_open(), the filp->private_data can be assigned the 'dir'
variable even if it was freed. This is on the error path, and is
harmless because the error return code will prevent filp->private_data
from being used. But for correctness, we should not assign it to
a recently freed variable, as that can cause static tools to give
false warnings.

Also have both subsystem_open() and system_tr_open() return -ENODEV
if tracing has been disabled.

Link: http://lkml.kernel.org/r/1383764571-7318-1-git-send-email-geyslan@gmail.com

Signed-off-by: Geyslan G. Bem <geyslan@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_events.c

@@ -1062,6 +1062,9 @@ static int subsystem_open(struct inode *inode, struct file *filp)
 	struct trace_array *tr;
 	int ret;
 
+	if (tracing_is_disabled())
+		return -ENODEV;
+
 	/* Make sure the system still exists */
 	mutex_lock(&trace_types_lock);
 	mutex_lock(&event_mutex);
@@ -1108,6 +1111,9 @@ static int system_tr_open(struct inode *inode, struct file *filp)
 	struct trace_array *tr = inode->i_private;
 	int ret;
 
+	if (tracing_is_disabled())
+		return -ENODEV;
+
 	if (trace_array_get(tr) < 0)
 		return -ENODEV;
 
@@ -1124,11 +1130,12 @@ static int system_tr_open(struct inode *inode, struct file *filp)
 	if (ret < 0) {
 		trace_array_put(tr);
 		kfree(dir);
+		return ret;
 	}
 
 	filp->private_data = dir;
 
-	return ret;
+	return 0;
 }
 
 static int subsystem_release(struct inode *inode, struct file *file)