CakePHP shell无限循环

I triggered CakePHP shell command in controller (AJAX POST call), and then the shell command ran into an infinite loop. I use the following code to print the trace.

$dt = debug_backtrace();
$cs = '';
foreach ($dt as $t) {
  $cs .= $t['file'] . ' line ' . $t['line'] . ' function ' . $t['function'] . "()
";
}
error_log($cs);

And I got the following results over and over again.

/public_html/lib/Cake/Controller/Controller.php line 490 function invokeArgs()
/public_html/lib/Cake/Routing/Dispatcher.php line 185 function invokeAction()
/public_html/lib/Cake/Routing/Dispatcher.php line 160 function _invoke()
/public_html/app/webroot/index.php line 108 function dispatch()

I also put console.log into the front end ajax, and the ajax call is only run once. And for some reason, the cakePHP repeats the ajax call again and again.

I have worked on this for a day now and I have no clue how to solve this. I use CakePHP 2.4.5, PHP 5.4.24

please help me on this!

Thanks in advance!