In our application we have the problem with high CPU load and hang process when upload of the file failed (user press Esc, network failure ....)

    def out(output = $stdout)
      convert_content_type!
      set_content_length!

      output.binmode      if output.respond_to?(:binmode)
      output.sync = false if output.respond_to?(:sync=)

      begin
        output.write(@cgi.header(@headers))

        if @cgi.send(:env_table)['REQUEST_METHOD'] == 'HEAD'
          return
        elsif @body.respond_to?(:call)
          # Flush the output now in case the @body Proc uses
          # #syswrite.
          output.flush if output.respond_to?(:flush)
          @body.call(self, output)
        else
          output.write(@body)
        end

        output.flush if output.respond_to?(:flush)
      rescue Errno::EPIPE, Errno::ECONNRESET
        # lost connection to parent process, ignore output
      end
    end

if connection to parent process is lost under passenger, then error from .flush is Errno::ESPIPE, not catched here, dispatch.rb catches it and calls failsafe_response. We happens to use "Exception Notifier" plugin, so we get the email with original error and process id and immediate look at the server shows that the process with this id is hanging with

_llseek(5, -1, 0xbfd03664, SEEK_CUR)    = -1 ESPIPE (Illegal seek)
_llseek(5, -1, 0xbfd03664, SEEK_CUR)    = -1 ESPIPE (Illegal seek)
_llseek(5, -1, 0xbfd03664, SEEK_CUR)    = -1 ESPIPE (Illegal seek)
_llseek(5, -1, 0xbfd03664, SEEK_CUR)    = -1 ESPIPE (Illegal seek)
_llseek(5, -1, 0xbfd03664, SEEK_CUR)    = -1 ESPIPE (Illegal seek)

module ActionController
  class CgiResponse
    def out_with_espipe(*args)
      begin
        out_without_espipe(*args)
      rescue Errno::ESPIPE => exception
        begin
          message    = exception.to_s + "\r\n" + exception.backtrace.join("\r\n")
          RAILS_DEFAULT_LOGGER.fatal(message)
          #NonwebNotifier.deliver_exception_notification(exception, {})
        rescue Exception => e
          $stderr.write("Exception #{e.to_s} in handling exception #{exception.to_s}")
        end
      end
    end
    alias_method_chain :out, :espipe
  end
end