tracing: Disable tracers before deletion of instance

When an instance is about to be deleted, make sure the tracer
is set to nop. If it isn't reset the tracer and set it to the nop
tracer, otherwise memory leaks and bad pointers may result.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -3907,6 +3907,23 @@ create_trace_option_files(struct trace_array *tr, struct tracer *tracer);
 static void
 destroy_trace_option_files(struct trace_option_dentry *topts);
 
+/*
+ * Used to clear out the tracer before deletion of an instance.
+ * Must have trace_types_lock held.
+ */
+static void tracing_set_nop(struct trace_array *tr)
+{
+	if (tr->current_trace == &nop_trace)
+		return;
+	
+	tr->current_trace->enabled = false;
+
+	if (tr->current_trace->reset)
+		tr->current_trace->reset(tr);
+
+	tr->current_trace = &nop_trace;
+}
+
 static int tracing_set_tracer(struct trace_array *tr, const char *buf)
 {
 	static struct trace_option_dentry *topts;
@@ -6142,6 +6159,7 @@ static int instance_delete(const char *name)
 
 	list_del(&tr->list);
 
+	tracing_set_nop(tr);
 	event_trace_del_tracer(tr);
 	debugfs_remove_recursive(tr->dir);
 	free_percpu(tr->trace_buffer.data);