ftrace: Only update the function code on write to filter files

If function tracing is enabled, a read of the filter files will
cause the call to stop_machine to update the function trace sites.
It should only call stop_machine on write.

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

kernel/trace/ftrace.c

@@ -2413,14 +2413,16 @@ ftrace_regex_release(struct inode *inode, struct file *file, int enable)
 		ftrace_match_records(parser->buffer, parser->idx, enable);
 	}
 
-	mutex_lock(&ftrace_lock);
-	if (ftrace_start_up && ftrace_enabled)
-		ftrace_run_update_code(FTRACE_ENABLE_CALLS);
-	mutex_unlock(&ftrace_lock);
-
 	trace_parser_put(parser);
 	kfree(iter);
 
+	if (file->f_mode & FMODE_WRITE) {
+		mutex_lock(&ftrace_lock);
+		if (ftrace_start_up && ftrace_enabled)
+			ftrace_run_update_code(FTRACE_ENABLE_CALLS);
+		mutex_unlock(&ftrace_lock);
+	}
+
 	mutex_unlock(&ftrace_regex_lock);
 	return 0;
 }