[alsa-devel] Something wrong with snd_pcm_avail_update

Takashi Iwai tiwai at suse.de
Wed Sep 24 09:56:29 CEST 2008

At Wed, 24 Sep 2008 02:19:54 +0200,
Lennart Poettering wrote:
> Heya!
> There seems to be something wrong with snd_pcm_update_avail() for mmap
> in recent 2.6.26 kernels:
> Quoting Alexander Gavrilov:
> <snip>
> Fedora 9 with kernel exhibits a bug where
> the driver decrements its hw.ptr under certain stress
> conditions, or at least it appears so from debugging.
> It causes alsa-lib to give absurdly huge avail numbers
> to pulseaudio, which crashes it. This patch adds a
> work-around to avoid such unfriendly behavior until
> the bug is fixed.
> As this is not a real fix, it displays a message every
> time it is activated.
> </snip>
> https://bugzilla.redhat.com/show_bug.cgi?id=462200
> (see the patch attached to that bug report)
> Takashi, Jaroslav, do you know anything about this?

The DMA position handling on some HD-audio hardware is unstable.
This could be a reason.

The latest 2.6.27-rc* kernel has a few workarounds for such.
Give it a try.


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