tracing: Clear all trace buffers when unloaded module event was used

Currently we do not know what buffer a module event was enabled in.
On unload, it is safest to clear all buffer instances, not just the
top level buffer.

Todo: Clear only the buffer that the event was used in. The
infrastructure is there to do this, but it makes the code a bit
more complex. Lets get the current code vetted before we add that.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -912,9 +912,15 @@ void tracing_reset_current(int cpu)
 	tracing_reset(&global_trace, cpu);
 }
 
-void tracing_reset_current_online_cpus(void)
+void tracing_reset_all_online_cpus(void)
 {
-	tracing_reset_online_cpus(&global_trace);
+	struct trace_array *tr;
+
+	mutex_lock(&trace_types_lock);
+	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
+		tracing_reset_online_cpus(tr);
+	}
+	mutex_unlock(&trace_types_lock);
 }
 
 #define SAVED_CMDLINES 128

kernel/trace/trace.h

@@ -496,7 +496,7 @@ int tracing_is_enabled(void);
 void tracing_reset(struct trace_array *tr, int cpu);
 void tracing_reset_online_cpus(struct trace_array *tr);
 void tracing_reset_current(int cpu);
-void tracing_reset_current_online_cpus(void);
+void tracing_reset_all_online_cpus(void);
 int tracing_open_generic(struct inode *inode, struct file *filp);
 struct dentry *trace_create_file(const char *name,
 				 umode_t mode,

kernel/trace/trace_events.c

@@ -1649,14 +1649,18 @@ static void trace_module_remove_events(struct module *mod)
 		list_del(&file_ops->list);
 		kfree(file_ops);
 	}
+	up_write(&trace_event_mutex);
 
 	/*
 	 * It is safest to reset the ring buffer if the module being unloaded
-	 * registered any events that were used.
+	 * registered any events that were used. The only worry is if
+	 * a new module gets loaded, and takes on the same id as the events
+	 * of this module. When printing out the buffer, traced events left
+	 * over from this module may be passed to the new module events and
+	 * unexpected results may occur.
 	 */
 	if (clear_trace)
-		tracing_reset_current_online_cpus();
-	up_write(&trace_event_mutex);
+		tracing_reset_all_online_cpus();
 }
 
 static int trace_module_notify(struct notifier_block *self,