[PATCH] ASoC: soc-pcm: fix fe and be race when accessing substream->runtime

[Pierre-Louis Bossart]

On 9/27/22 14:30, Eugeniu Rosca wrote:
> Hi Pierre,
> 
> On Di, Sep 27, 2022 at 09:51:46 +0200, Pierre-Louis Bossart wrote:
>> On 9/26/22 18:35, Eugeniu Rosca wrote:
>>> From: xiao jin <jin.xiao at intel.com>
>>>
>>> After start of fe and be, fe might go to close without triggering
>>> STOP, and substream->runtime is freed. However, be is still at
>>> START state and its substream->runtime still points to the
>>> freed runtime.
>>>
>>> Later on, FE is opened/started again, and triggers STOP.
>>> snd_pcm_do_stop => dpcm_fe_dai_trigger
>>>                 => dpcm_fe_dai_do_trigger
>>>                 => dpcm_be_dai_trigger
>>>                 => dpcm_do_trigger
>>>                 => soc_pcm_trigger
>>>                 => skl_platform_pcm_trigger
>>> skl_platform_pcm_trigger accesses the freed old runtime data and
>>> kernel panic.
>>>
>>> The patch fixes it by assigning be_substream->runtime in
>>> dpcm_be_dai_startup when be's state is START.
>>
>> Can I ask on which kernel this patch was validated and on what platform?
> 
> As shared with Czarek in https://lore.kernel.org/alsa-devel/20220927110022.GA3802@lxhi-065/ ,
> this patch was originally extracted from the out-of-tree Intel Apollo
> Lake v4.1 KNL releases, hence it was validated on Intel ref.boards.
> 
> No re-testing/re-validation has been performed on the latest vanilla.

There's no way to predict how a patch for a kernel 4.1 - released 7
years ago - would behave with a new kernel. If it's not tested it cannot
be merged.

> One of the goals behind submitting the patch is getting in touch
> with the original authors, as well as the members of alsa-devel,
> to assess if the patch is still relevant.

The only thing we could do is have more clarity on the test case and try
to reproduce it.

>>
>> We've done a lot of work since last year on DPCM states, 
> 
> Could you please feedback if the work on the DPCM states is
> pre- or post-v5.10?

It doesn't matter for this discussion on the upstream kernel. But yes
it's post v5.10.

> 
>> and I wonder
>> the problem mentioned above actually exists on recent kernels.
>>
>> Specifically, if the FE is closed, I don't get how the BE is not closed
>> as well. And if this problem is found on a recent kernel, then it should
>> be seen in the AVS driver as well, no?
> 
> It is totally conceivable (if not very likely) that the mainline
> advancements in the sound subsystem make this patch obsolete.
> 
> I would be happy if that's the final outcome of our discussion
> (since this will allow dropping the patch in our downstream kernel).
> 
> Best Regards,
> Eugeniu