Re: [PATCH] ALSA: hda: Do not unset preset when cleaning up codec

[Cezary Rojewski <cezary.rojewski@intel.com>]

On 2023-01-17 5:01 PM, Takashi Iwai wrote:

...

>> This is a continuation of a discussion that begun in the middle of 2022
>> [1] and was part of a larger series addressing several HDAudio topics.
>>
>> Single rmmod on ASoC's codec driver module is enough to cause a panic.
>> Given our results, no regression shows up with modprobe/rmmod on
>> snd_hda_intel side with this patch applied.
> 
> I think one possible regression by this change would be the case you
> reload another codec driver.  With keeping codec->preset, it's still
> thought as if already matched, and a wrong one could be used.
> 
> And, this would be nothing but a leak of the possibly freed address.
> After hda_codec_driver_remove(), card->preset may point to an already
> freed address.
> 
> So, just removing isn't right.  It has to be cleared somewhere
> instead, e.g. in hda_bind.c.
> 
> But, one thing I'm still concerned is that your comment about the call
> without the card binding.  Do you mean that the
> snd_hda_codec_cleanup_for_unbind() may be called even if codec->card
> isn't set?

One proposition would be to add line:
	codec->preset = NULL;

after both invocations of snd_hda_codec_cleanup_for_unbind() in 
hda_codec_driver_probe/remove() in sound/pci/hda/hda_bind.c.

In regard to your last question - no, cleanup is only called either in 
component->probe()'s error path or in component->remove() once 
snd_hda_codec_device_new() succeeds and thus, codec->card points to a 
valid sound card.

What I meant by my comment, is that removal of any components of an ASoC 
sound card will cause all other components to have their ->remove() op 
called too. Let's say I unload snd_soc_avs_hdaudio module without 
unloading snd_soc_avs. As bus (snd_soc_avs) owns the codecs, its 
platform component->remove() gets called right after codec 
component->remove() but the actual devices are still present in the 
system even with the sound card module (snd_soc_avs_hdaudio) unloaded.


Regards,
Czarek