Re: [ecasound] Re: Bug#317900: ecasound freezes the computer under root with double buffering

From: Kai Vehmanen <kvehmanen@email-addr-hidden>
Date: Tue Jul 12 2005 - 23:05:09 EEST

Hello all,

On Wed, 13 Jul 2005, Junichi Uekawa wrote:

> It sounds possible, considering the privilege it is running under,
> but nasty.
>> If ecasound runs with double buffering and under root, almost any kind
>> of termination of the process causes complete computer freeze:
>> /usr/bin/ecasound -b:4096 -z:db,661500 -r:99 -f:16,2,44100,i -i
>> alsahw,0,0 -o stdout

couple of notes:
- -r:99 is very extreme and dangerous, please use the default "-r"
   or just a lower value like "-r:40"
- -z:db,661500 is a _lot_ of buffering (15secs of audio at 44.1kHz),
    but might be needed on some machines

And then a couple of questions:

- which version of ecasound? (if old 2.0.x release, please upgrade
   to newer 2.2 (in sarge) and retry the tests, 2.0.x is really old
   and not supported anymore)
- which soundcard...? the problem description sounds like a driver
   problem (running with -r, i.e. SCHED_FIFO scheduling, can turn
   a minor driver bug into a system-freeze type of problem)

I've tested the above configuration myself on multiple machines and no
freezes so far, no matter what I try.

>> It exits properly, if I stop it as follows:
>> killall -STOP ecasound; killall -KILL ecasound
>> Another way to stop ecasound safely is to run it with tee like this:
>> /usr/bin/ecasound -b:4096 -z:db,661500 -r:99 -f:16,2,44100,i -i
>> alsahw,0,0 -o stdout | tee audio.raw > /dev/null

Hmm, this is interesting. The signal handling has been changed
a few times since 2.0.x -- if you are running 2.0.x, that might
explain the problem. Otherwise further investigation is definitely
needed. The bad news is that tracking down SCHED_FIFO-triggere problems
can be very difficult.. :(

>> Looks like ecasound does not tolerate any signal when it is in system
>> call (read kernel mode) of any kind.

This should not be the case. The signal handler is designed to be
real-time safe, and should be able to cleanly shutdown the engine in all
possible cases. But, but, obviously something goes badly wrong in your

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Received on Wed Jul 13 00:15:17 2005

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