for the ones having problems with the headphones jack in the sony vaio FZ21M, I've taken the following process that resolved the problem:

  1. Edit /etc/modprobe.d/alsa-base (sudo gedit /etc/modprobe.d/alsa-base) and add this in the bottom of it

        options snd-hda-intel model=vaio

  2. sudo apt-get install linux-backports-modules-$(uname -r)

  3. reboot your system.

see the full discussion here.