[alsa-devel] Assertion failure in alsa-lib crashing applications (snd_pcm_area_copy: Assertion `dst < src || dst >= src + bytes' failed)

[Takashi Iwai]

On Wed, 29 Jun 2016 15:59:59 +0200,
Baptiste Jonglez wrote:
> 
> Hello Takashi,
> 
> On Wed, Jun 29, 2016 at 03:39:37PM +0200, Takashi Iwai wrote:
> > > Do you think the problem is likely to come from an incorrect API usage
> > > from the application?  Knowing this would significantly narrow down the
> > > search, because the problem could also come from within alsa itself.
> > > 
> > > The callling code from the application is quite complex, see here:
> > > 
> > >   https://github.com/savoirfairelinux/ring-daemon/blob/master/src/media/audio/alsa/alsalayer.cpp
> > > 
> > > In particular, the assertion is triggered by the call to
> > > snd_pcm_avail_update() at line 694 (see the stack trace below).
> > 
> > I have too little time to investigate on this issue, but judging from
> > the fact that there has been no such a report until now, I guess it's
> > specific to your code.  But I can't say sure, of course.
> 
> Well, I did find other projects having this issue:
> 
> https://aur.archlinux.org/packages/zoom/#comment-544696
> http://ubuntuforums.org/showthread.php?t=2248373
> https://github.com/js-platform/node-webrtc/issues/110
> https://fedorahosted.org/fldigi/ticket/70

Oh well.  They have been never reported to upstream...
In anyway, your report is the first one, and with a stack trace.

> Although in most of these cases, the issue seems 100% reproducible
> (e.g. crash at startup).  In our case, the assertion failure only happens
> when there is significant CPU load.
> 
> > Is the relevant code path accessed concurrently?  The possible race is
> > the first suspect I'd always think of in such a case.
> 
> Good idea, I will check.  Given it happens when the CPU is loaded, my
> guess is that "something" is done too late, which means that it works on
> "invalidated" data (this is all very vague, sorry).
> 
> Would you know a simple program using alsa-lib for sound capture, with
> which I could try to reproduce?

arecord?  But it's no multi-thread, so not suitable for the
concurrency tests.

How is your PCM plugin setup?  Is softvol over dmix?


Takashi