Comment 38 for bug 1203520

Stable Release Update (SRU) & bug control nomination request:

[Impact]
Playing sound, opening pavucontrol mixer or hotplugging HDMI sink hard-freezes Ubuntu 12.04 LTS unless module snd_hda_codec_hdmi is blacklisted.
This is neither a workaround nor remedy, as additional digital sound cards would have to be installed (and fine-tuned for delay compensation) to re-establish required functionality thus removed from HDMI.
Similar issue exists in https://bugs.launchpad.net/bugs/1169984 & duplicates, potentially making access to display or even surround amplifier a DoS vector.

[Test Case]
While running speaker-test, VLC, Xine or other sound sources, open pavucontrol or connect another monitor/amplifier combination that is a sound sink with different speaker setup.
Playing sound before and after amplifier is turned on may suffice to reproduce crash, but no 100% trigger has been found yet.

[Regression Potential]
Per https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1169984/comments/124 the bug may actually be the regression.
Current situation is to risk severe crashes (for reasons inscrutable to average users) or lack proper audio (after module blacklisting, which also not feasible for many end users).
Avenue&side effects to potential fix yet to be determined.

[Other Info]
VDR / Home Theater systems presumably have to remain on 12.04 LTS for years.
Proprietary Nvidia driver may be implicated.