For the last few days I've been searching for more information to confirm this bug. Some users of other distros confirmed this to be a problem too.
With the latest kernels and alsa versions when alsa is under heavy load (for example playing 10 or 20 sounds simultaneously) it can freeze the whole system without any trace in the logs. The symptoms are quite strange for example you can run xterm but you can't run ps fax, shutdown hangs up after sending kill signal, etc.
I've found alsa bug report that also describes this very well including steps to reproduce this:
https://bugtrack.alsa-project.org/alsa- … php?id=761
Looks like an upstream problem to me so I'm not going to open arch bug report for now. I'm posting this FYI becasue it can be hard to identify what caused system freeze.
Unfortunatelly there is no cure for this bug (yet) - except (as I've been told by some users) downgrading alsa driver (alsa tools are ok).
If you know of any patches, fixes or workarounds please post the links here.
I'm using SB Live 5.1 but it seems that sound hardware is not important.