[alsa-lib] Query regarding snd_config_update_free_global() and threads etc.

[alsa-lib] Query regarding snd_config_update_free_global() and threads etc.

[Colin Guthrie]

Hi there,

I've got a (hopefully quick) query about snd_config_update_free_global()
and it's general thread safetyness.


I'm currently going insane on this bug:
https://bugs.kde.org/show_bug.cgi?id=232068
which revolves around a bug manifested in snd_pcm_close() (or rather
snd_pcm_ioplug_close()) when dealing with the ALSA->PulseAudio plugin.

>From what I can gather, this problem is related to a KDE module that is
loaded into the library in question which does some alsa probing and
ultimately calls snd_config_update_free_global() several times. The
library itself then goes on to use GStreamer to do actual audio output.
The crash then manifests itself prior to any sound actually being output.

I can reliably reproduce the machine on two machines (I don't have many
at my disposal), but cannot reproduce on a third. The two I can
reproduce it on are two and four core intel duo's. The one I cannot
reproduce on is an older, single core machine. I am leaning towards some
kind of thread safety issue.


In searching for similar problems, I found several references to similar
crashes attributed to snd_dlobj_cache_cleanup() perhaps not being thread
safe.

e.g.:
https://bugzilla.redhat.com/show_bug.cgi?id=482797#c14
 and
http://osdir.com/ml/attachments/txtpisfDmzbcN.txt
(and from that:
https://bugtrack.alsa-project.org/alsa-bug/view.php?id=2124
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=589896
)


I've found that removing the calls to
snd_config_update_free_global() avoid the issue. I'm not even sure they
are needed, but all the same I wanted to discuss the core issue.

The MEMORY-LEAK file suggests that it should only be called after all
snd_*_open() calls, but it doesn't indicate if this is just a
recommendation or mandatory.  Is the *only* purpose of this call to make
valgrind happy? Or does it serve some other useful purpose too?

Col



-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

Day Job:
  Tribalogic Limited [http://www.tribalogic.net/]
Open Source:
  Mandriva Linux Contributor [http://www.mandriva.com/]
  PulseAudio Hacker [http://www.pulseaudio.org/]
  Trac Hacker [http://trac.edgewall.org/]

Re: [alsa-lib] Query regarding snd_config_update_free_global() and threads etc.

[Jaroslav Kysela]

On Mon, 23 Aug 2010, Colin Guthrie wrote:

> Hi there,
>
> I've got a (hopefully quick) query about snd_config_update_free_global()
> and it's general thread safetyness.
>
>
> I'm currently going insane on this bug:
> https://bugs.kde.org/show_bug.cgi?id=232068
> which revolves around a bug manifested in snd_pcm_close() (or rather
> snd_pcm_ioplug_close()) when dealing with the ALSA->PulseAudio plugin.
>
>> From what I can gather, this problem is related to a KDE module that is
> loaded into the library in question which does some alsa probing and
> ultimately calls snd_config_update_free_global() several times. The
> library itself then goes on to use GStreamer to do actual audio output.
> The crash then manifests itself prior to any sound actually being output.
>
> I can reliably reproduce the machine on two machines (I don't have many
> at my disposal), but cannot reproduce on a third. The two I can
> reproduce it on are two and four core intel duo's. The one I cannot
> reproduce on is an older, single core machine. I am leaning towards some
> kind of thread safety issue.
>
>
> In searching for similar problems, I found several references to similar
> crashes attributed to snd_dlobj_cache_cleanup() perhaps not being thread
> safe.

I tried to work on snd_dlobj_cache issues. Please, could you test this 
patch?

http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=91c9c8f1b85e69b4bdc94a777d2767c4906c3f47

 					Thanks,
 						Jaroslav

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

Re: [alsa-lib] Query regarding snd_config_update_free_global() and threads etc.

[Colin Guthrie]

'Twas brillig, and Jaroslav Kysela at 23/08/10 16:13 did gyre and gimble:
> On Mon, 23 Aug 2010, Colin Guthrie wrote:
> 
>> Hi there,
>>
>> I've got a (hopefully quick) query about snd_config_update_free_global()
>> and it's general thread safetyness.
>>
>>
>> I'm currently going insane on this bug:
>> https://bugs.kde.org/show_bug.cgi?id=232068
>> which revolves around a bug manifested in snd_pcm_close() (or rather
>> snd_pcm_ioplug_close()) when dealing with the ALSA->PulseAudio plugin.
>>
>>> From what I can gather, this problem is related to a KDE module that is
>> loaded into the library in question which does some alsa probing and
>> ultimately calls snd_config_update_free_global() several times. The
>> library itself then goes on to use GStreamer to do actual audio output.
>> The crash then manifests itself prior to any sound actually being output.
>>
>> I can reliably reproduce the machine on two machines (I don't have many
>> at my disposal), but cannot reproduce on a third. The two I can
>> reproduce it on are two and four core intel duo's. The one I cannot
>> reproduce on is an older, single core machine. I am leaning towards some
>> kind of thread safety issue.
>>
>>
>> In searching for similar problems, I found several references to similar
>> crashes attributed to snd_dlobj_cache_cleanup() perhaps not being thread
>> safe.
> 
> I tried to work on snd_dlobj_cache issues. Please, could you test this 
> patch?
> 
> http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=91c9c8f1b85e69b4bdc94a777d2767c4906c3f47

Sure, will try and do so this evening and report back. Thanks!

Col

-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

Day Job:
  Tribalogic Limited [http://www.tribalogic.net/]
Open Source:
  Mandriva Linux Contributor [http://www.mandriva.com/]
  PulseAudio Hacker [http://www.pulseaudio.org/]
  Trac Hacker [http://trac.edgewall.org/]

Re: [alsa-lib] Query regarding snd_config_update_free_global() and threads etc.

[Colin Guthrie]

'Twas brillig, and Colin Guthrie at 23/08/10 16:49 did gyre and gimble:
> 'Twas brillig, and Jaroslav Kysela at 23/08/10 16:13 did gyre and gimble:
>> On Mon, 23 Aug 2010, Colin Guthrie wrote:
>>
>>> Hi there,
>>>
>>> I've got a (hopefully quick) query about snd_config_update_free_global()
>>> and it's general thread safetyness.
>>>
>>>
>>> I'm currently going insane on this bug:
>>> https://bugs.kde.org/show_bug.cgi?id=232068
>>> which revolves around a bug manifested in snd_pcm_close() (or rather
>>> snd_pcm_ioplug_close()) when dealing with the ALSA->PulseAudio plugin.
>>>
>>>> From what I can gather, this problem is related to a KDE module that is
>>> loaded into the library in question which does some alsa probing and
>>> ultimately calls snd_config_update_free_global() several times. The
>>> library itself then goes on to use GStreamer to do actual audio output.
>>> The crash then manifests itself prior to any sound actually being output.
>>>
>>> I can reliably reproduce the machine on two machines (I don't have many
>>> at my disposal), but cannot reproduce on a third. The two I can
>>> reproduce it on are two and four core intel duo's. The one I cannot
>>> reproduce on is an older, single core machine. I am leaning towards some
>>> kind of thread safety issue.
>>>
>>>
>>> In searching for similar problems, I found several references to similar
>>> crashes attributed to snd_dlobj_cache_cleanup() perhaps not being thread
>>> safe.
>>
>> I tried to work on snd_dlobj_cache issues. Please, could you test this 
>> patch?
>>
>> http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=91c9c8f1b85e69b4bdc94a777d2767c4906c3f47
> 
> Sure, will try and do so this evening and report back. Thanks!

That patch (along with 09879a4bb58199f64abcb8df506f917c8efc2383: pcm:
add defaults.pcm.minperiodtime parsing - just to avoid conflicts) on top
of 1.0.23 seems to fix the easily reproducible crash case for me. \o/

Awesome. Thanks!

Col

-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

Day Job:
  Tribalogic Limited [http://www.tribalogic.net/]
Open Source:
  Mandriva Linux Contributor [http://www.mandriva.com/]
  PulseAudio Hacker [http://www.pulseaudio.org/]
  Trac Hacker [http://trac.edgewall.org/]