Something wrong with snd_pcm_avail_update

Something wrong with snd_pcm_avail_update

[Lennart Poettering]

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 2.6.26.3-29 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?

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

Re: Something wrong with snd_pcm_avail_update

[Takashi Iwai]

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 2.6.26.3-29 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.


Takashi

Re: Something wrong with snd_pcm_avail_update

[Jaroslav Kysela]

On Wed, 24 Sep 2008, 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 2.6.26.3-29 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?

If it's HDA hardware, the user might try to test the recent linux kernels 
or the ALSA driver compiled from tarball available on 
www.alsa-project.org. The hw position routines were improved recently for 
the HDA driver.

					Jaroslav

-----
Jaroslav Kysela <perex@perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.