Hello,

Takashi Iwai wrote, on 05/25/12 09:25:
> At Wed, 23 May 2012 13:26:57 -0700,
> Tejun Heo wrote:
>>
>> Cc'ing Takashi.  Hi!
> 
> Also Cc'ed Fengguang, who worked on ELD stuff.
> 
>> On Wed, May 23, 2012 at 09:56:36PM +0200, Jörg-Volker Peetz wrote:
>>> May 23 21:32:33 hostname kernel: XXX delayed_work_timer_fn: cwq
>>> (null), fn=hdmi_repoll_eld
>>
>> So, we have the winner.
>>
>> Takashi, sound/pci/hda/patch_hdmi.c::hdmi_repoll_eld() is causing
>> workqueue code dereference %NULL pointer.  It *looks* like something
>> is corrupting the work item while it's queued.  It could be a
>> workqueue bug but I don't think that's likely - the code has been
>> stable for quite some time now.  I glanced through the code and
>> nothing stands out.  Does something ring a bell?
> 
> I also don't know of this problem.  My initial thought was that the
> work struct placed right after sink_eld in struct hdmi_spec_per_pin is
> overwritten wrongly by reading some ELD data.  But I failed to spot
> out the bug...
> 
> Reading back through the thread, the problem seems triggered via usb
> video cam.  I wonder how this is connected to the HDMI audio.
> 
> To get things straight: does this bug happen even without HDMI, DP or
> DVI cable plugged, i.e. only with the laptop without connecting to the
> external digital output?
> 
yes it happens without any HDMI cable plugged. The notebook is only connected to
an ethernet cable and the power cable. I'll append /var/log/dmesg, it also
contains the kernel command line with "radeon.audio=1".

The computer has two graphic chips:
ATI Mobility Radeon HD 4200 integrated graphics (non-free firmware R600_rlc.bin)
ATI Mobility Radeon HD 5470 graphic (512MB) (non-free firmware CEDAR_*.bin)
During booting, the discrete GPU is switched off using vga switcheroo:

$ mount -t debugfs none /sys/kernel/debug
$ echo -n OFF > /sys/kernel/debug/vgaswitcheroo/switch

For the sound kernel module the following options are set in
/etc/modprobe.d/alsa-base.conf:

options snd-hda-intel model=hp-dv7-4000 enable_msi=1

> 
>>> (without line-break).
>>>
>>> By the way, don't know if this is related, I have a phenomenon with a spurious
>>> interrupt with every linux version I've used before on this notebook. Half a
>>> minute after starting the system the computer produces approx. 220 lines like
>>>
>>> ... kernel: hda-intel: spurious response 0x0:0x0, last cmd=0x170503
>>>
>>> Now with 3.4.0, I see an additional message right before (the minute before) the
>>> "XXX ..." line:
>>>
>>> ...kernel: hda_intel: azx_get_response timeout, switching to single_cmd mode:
>>> last cmd=0x003f0900
>>
>> These too seem to be for you, Takashi. :)
> 
> This means essentially the codec communication got stalled.  This is a
> bad signal.  It happens often with a wrong HD-audio verb, but often
> with a bad IRQ, whatever.
> 
> I'd need alsa-info.sh output (run with --no-upload option) for further
> analysis.
> 
> 
> thanks,
> 
> Takashi

My first try to run the alsa-info.sh script with the plain 3.4 kernel produced
the same kernel oops freezing the notebook (and /tmp is mounted on tmpfs).
Therefore I applied the patch from Tejun to produce a usable output.
I attach it also. As you will notice, it contains the line beginning with "XXX"
due to Tejun's patch.

Thank you all for your help.
-- 
Best regards,
Jörg-Volker.