Ubuntu 14.04 php5-fpm throws unknown instance on service restart

After upgrading my Ubuntu server from 12.04 to 14.04 this morning, I tried to restart php5-fpm and got this error:

Unknown job: php5-fpm

It is a Ubuntu's bug: https://bugs.launchpad.net/ubuntu/+source/php5/+bug/1272788/

One workaround that works for me is:

Create /etc/init/php5-fpm.override file with the single line "reload signal USR2" in it.

Reference: http://stackoverflow.com/questions/19998526/ubuntu-php5-fpm-throws-unknown-instance-on-reload