Using kernel 2.6.29-rc1 the system fails to shutdown (reboot or halt) since it waits for alsasound to stop indefinitely. The last thing printed by alsasound is "Unloading Alsa modules". I was able to manually unload the driver using rmmod -f snd-hda-intel and then shutdown worked fine.
Some investigation showed that the command that waits indefinitely is rmmod --wait snd_hda_codec_idt and this is because it is used by snd-hda-intel which is still loaded. What (I think) should really happen is modprobe -r snd-hda-intel which will unload all relevant modules. I guess this module was added in 2.6.29-rc1 and that's why I haven't seen this in previous versions.
Indeed, as HD-Audio got modularised the ordering in which modules are unloaded became more important. This meant that the brittle code that automatically unloaded modules broke down further and in more interesting ways. As ALSA upstream noted, it is a particularly silly idea to automatically unload modules prior to system shutdown. As such, we have turned it off and will be deleting it soon. Sorry for the inconvenience. (As your bug report is pretty much identical to an earlier report, I am marking it a duplicate) *** This bug has been marked as a duplicate of bug 253535 ***
