heat-config can't exit due to <defunct> process

[Long Quan Sha]

When I use heat OS::Heat::SoftwareDeployment to deploy a script to config a vm which uses fedora 20 image, the deploy script is to start a simple web server, I found the script is invoked by /var/lib/heat-config/hooks/script, but it generates a <defunct> process, can't exit, as a result, stack deployment is failed with time out error.

config script is like below:
  setup_web:
    type: OS::Heat::SoftwareConfig
    properties:
          template: |
            #!/bin/bash
            echo "start web server" >>/tmp/deploy.log
             python -m SimpleHTTPServer 80 &
            exit 0
    group: script

deployment process in vm:

root 1079 908 0 02:06 ? 00:00:01 /opt/stack/venvs/os-refresh-config/bin/python /usr/local/bin/os-refresh-config
root 1092 1079 0 02:06 ? 00:00:00 /bin/bash /usr/local/bin/dib-run-parts /usr/libexec/os-refresh-config/configure.d
root 1118 1092 0 02:06 ? 00:00:02 python /usr/libexec/os-refresh-config/configure.d/55-heat-config
root 1121 1118 0 02:06 ? 00:00:01 python /var/lib/heat-config/hooks/script
root 1122 1121 0 02:06 ? 00:00:00 [76e823d2-0bf1-4] <defunct>
root 1134 1 0 02:07 ? 00:00:00 python -m SimpleHTTPServer 80