[alsa-devel] [BUG] Kernel crash on Allwinner H3 due to sound core changes

[Kuninori Morimoto]

Hi Jernej

Thank you for your hard work

> I found the issue. Commit be7ee5f32a9a ("ASoC: soc-generic-dmaengine-pcm: 
> replace platform to component") changes struct dmaengine_pcm:
> 
>  struct dmaengine_pcm {
>  	struct dma_chan *chan[SNDRV_PCM_STREAM_LAST + 1];
>  	const struct snd_dmaengine_pcm_config *config;
> -	struct snd_soc_platform platform;
> +	struct snd_soc_component component;
>  	unsigned int flags;
>  };
> 
> In snd_dmaengine_pcm_register():
> ret = snd_soc_add_component(dev, &pcm->component,
> 				    &dmaengine_pcm_component, NULL, 0);
> 
> And now, sun4i-codec first time returns -EPROBE_DEFER since driver for analog 
> part is not yet loaded. Because of that, all components get destroyed.
> 
> snd_dmaengine_pcm_unregister() calls snd_soc_unregister_component() and that 
> one calls __snd_soc_unregister_component() multiple times (until it fails).
> 
> Issue is that __snd_soc_unregister_component() uses kfree() on component 
> pointer and that naturally can't succed since component was never kmalloc'ed 
> since it is a part of a bigger structure - struct dmaengine_pcm.
> 
> What would be the best fix? Changing struct dmaengine_pcm to have pointer to a 
> component, so it can be freed?

Ahh.. indeed. Good catch !
How about to add such flag ?
This is just idea. No tested, No compiled, but can help you ?

One note here is that reusing "registered_as_component" flag is
not good idea, because it will be removed
when platform/codec were removed

------------------------
diff --git a/include/sound/soc.h b/include/sound/soc.h
index 1a73232..b9b1b4c 100644
--- a/include/sound/soc.h
+++ b/include/sound/soc.h
@@ -853,6 +853,7 @@ struct snd_soc_component {
 	unsigned int ignore_pmdown_time:1; /* pmdown_time is ignored at stop */
 	unsigned int registered_as_component:1;
 	unsigned int suspended:1; /* is in suspend PM state */
+	unsigned int alloced_component:1;
 
 	struct list_head list;
 	struct list_head card_aux_list; /* for auxiliary bound components */
diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index c0edac8..0e33bcf 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -3492,6 +3492,7 @@ int snd_soc_register_component(struct device *dev,
 	if (!component)
 		return -ENOMEM;
 
+	component->alloced_component = 1;
 	return snd_soc_add_component(dev, component, component_driver,
 				     dai_drv, num_dai);
 }
@@ -3523,7 +3524,9 @@ static int __snd_soc_unregister_component(struct device *dev)
 
 	if (found) {
 		snd_soc_component_cleanup(component);
-		kfree(component);
+
+		if (component->alloced_component)
+			kfree(component);
 	}
 
 	return found;
------------------------