[PATCH] ALSA: core: Warn on empty module

[Pierre-Louis Bossart]

On 6/24/20 11:03 AM, Takashi Iwai wrote:
> The module argument passed to snd_card_new() must be a valid non-NULL
> pointer when the module support is enabled.  Since ASoC driver passes
> the argument from each snd_soc_card definition, one may forget to set
> the owner field and lead to a NULL module easily.
> 
> For catching such an overlook, add a WARN_ON() in snd_card_new().
> Also, put the card->module assignment in the ifdef block for a very
> minor optimization.
> 
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
> ---
>   sound/core/init.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/sound/core/init.c b/sound/core/init.c
> index b02a99766351..0478847ba2b8 100644
> --- a/sound/core/init.c
> +++ b/sound/core/init.c
> @@ -203,7 +203,10 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
>   	mutex_unlock(&snd_card_mutex);
>   	card->dev = parent;
>   	card->number = idx;
> +#ifdef MODULE
> +	WARN_ON(!module);
>   	card->module = module;
> +#endif
>   	INIT_LIST_HEAD(&card->devices);
>   	init_rwsem(&card->controls_rwsem);
>   	rwlock_init(&card->ctl_files_rwlock);

Would it make sense to also change the ASoC code to use THIS_MODULE 
instead of card->owner?

/* card bind complete so register a sound card */
ret = snd_card_new(card->dev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1,
		card->owner, 0, &card->snd_card);

A quick grep shows we are setting .owner = THIS_MODULE pretty much all 
the time for machine drivers.