There are similar questions like this, this, and this.
None help because the goal is to prevent logging of long parameters within a specific action instead of using config.filter_parameters. Also the answer must work for Rails 3.2.x while many answers are based on Rails 5.
One answer suggests calling request.filtered_parameters inside the controller method, but calling request.filtered_parameters.delete :long_param did not stop :long_param from getting logged.
config.filter_parameters takes a lambda function, so you can filter whatever you want. See answers here and here.
If you only want to filter long arguments for a specific action, well, you are making your life unnecessarily complicated. Either filter all long parameters, using your lambda to set a limit on parameter value length, or change the parameter key of the action you want to filter so that it is unique and and then just filter by that key.