Bug#753816: [systemd] Broken audio

[Ben Hutchings]

On Sat, 2014-07-05 at 18:58 +0200, Michael Biebl wrote:
> Am 05.07.2014 18:38, schrieb Antonio Marcos López Alonso:
> > El 05/07/14 17:06, Michael Biebl escribió:
> >> Am 05.07.2014 17:56, schrieb Antonio Marcos López Alonso:
> >>> Just in case, have you noticed I'm using an ALSA-Jack loopback setting
> >>> for audio?
> >> Under sysvinit, udev (including udevadm settle) is started before the
> >> kmod init script, which loads snd_aloop.
> >> That means, snd_aloop is loaded after snd_hda_intel.
> >>
> >> Under systemd, it looks like the snd_aloop module is loaded about the
> >> same time systemd-udevd is started. There might be a race here and
> >> snd_aloop is loaded before snd_hda_intel.
> >>
> >> This *might* be the reason, but I'm no expert on this matter.
> >>
> >> Can you try removing snd_aloop from /etc/modules and test if that makes
> >> a difference.
> >>
> > 
> > OK removed snd_aloop and audio is back. Then reloaded the module,
> > restarted JACK and audio is still fine. So as you said there must be
> > some race condition in there. Should I keep this ticket opened?
> > 
> 
> Hm, not sure what to do about this. We could order
> systemd-load-modules.service after systemd-udevd.service. But that
> doesn't guarantee the loading order of the modules and it feels like
> papering over the underlying issue.
> 
> I'm no sound expert, but I'd say that the loading order should not
> matter. Maybe we need some input from the kernel team or some alsa
> experts here.

I think this is due to ALSA userland (or maybe higher levels) being
stupid about device selection.  I think the default is to use sound
device 0, which can be whichever driver won the race.

> I took the liberty to CC the Debian kernel team and the maintainer of
> the snd_aloop module. I hope they can help us here.
> 
> For reference the complete bug report is at [1]
> 
> 
> Michael
> 
> 
> [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=753816

I think the usual workaround is to add 'index=1' to the snd-aloop line
in /etc/modules.  It is probably possible to do something more
sophisticated in an ALSA configuration file.

Ben.

-- 
Ben Hutchings
The most exhausting thing in life is being insincere. - Anne Morrow Lindberg
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