Bug#828190: this bug (pulseaudio) actually breaks unrelated software

[Harald Geyer]

Hi,

I have been wrong in at least one part of my previous update to this
bug. Even if I stop all threads in the sound application (in my case
baresip) in the debugger, pulseaudio still run's at 100% CPU spamming
syslog. Only killing baresip (probably the closing of file descriptors)
makes pulseaudio recover.

I got confused, because somehow this situation causes an other thread
of baresip consume lot's of CPU, which made me believe that there is
a rather tight loop between baresip and pulseaudio. Actually the calls
to the sound API never return while pulseaudio is busy, thus the
application never get's an error and can't actually close its ALSA
handles.

So at this point I'm convinced the entire problem is within pulseaudio.
Since baresip is not a pulseaudio but an ALSA application, works fine
without pulseaudio installed and only uses pulseaudio because
pulseaudio makes itself the default ALSA device on installation, I think
it is fair to say that pulseaudio is breaking unrelated software here.

I'm tempted to raise the severity of this bug to release critical, but
I guess this should be at the discretion of the maintainers.

This is clearly a (probably rather old) upstream bug. It seems to mostly
manifest itself with SoC devices, which might explain why it is more
often seen recently and with debian: Debian arm ports are quite popular
with users of SoC based laptops.

>From the debian packaging PoV I can see two possible workarounds:
* Disable sample rate switching by setting defaut-sample-rate and
  alternate-sample-rate to the same value by default for the ARM based
  ports and prominently document the problem for everybody else.
* Don't enable pulseaudio at all on ARM based ports without some kind
  of manual intervention by the local admin.

HTH,
Harald

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