staging: greybus: Avoid abusing controls_rwsem

The controls_rwsem of snd_card object is rather an internal lock, and
not really meant to be used by others for its data protection.

This patch addresses it by replacing the controls_rwsem usages with
the own (new) mutex.

Note that the up_write() and down_write() calls around
gbaudio_remove_component_controls() are simply dropped without
replacement.  These temporary up/down were a workaround since
gbaudio_remove_component_controls() itself took the rwsem.  Now it was
also gone, we can clean up the workaround, too.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Vaibhav Agarwal <vaibhav.sr@gmail.com>
Cc: Mark Greer <mgreer@animalcreek.com>
Cc: Johan Hovold <johan@kernel.org>
Cc: Alex Elder <elder@kernel.org>
Cc: greybus-dev@lists.linaro.org
Link: https://lore.kernel.org/r/20230718141304.1032-8-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

drivers/staging/greybus/audio_codec.c

@@ -807,7 +807,6 @@ int gbaudio_register_module(struct gbaudio_module_info *module)
 {
 	int ret;
 	struct snd_soc_component *comp;
-	struct snd_card *card;
 	struct gbaudio_jack *jack = NULL;
 
 	if (!gbcodec) {
@@ -816,21 +815,20 @@ int gbaudio_register_module(struct gbaudio_module_info *module)
 	}
 
 	comp = gbcodec->component;
-	card = comp->card->snd_card;
 
-	down_write(&card->controls_rwsem);
+	mutex_lock(&gbcodec->register_mutex);
 
 	if (module->num_dais) {
 		dev_err(gbcodec->dev,
 			"%d:DAIs not supported via gbcodec driver\n",
 			module->num_dais);
-		up_write(&card->controls_rwsem);
+		mutex_unlock(&gbcodec->register_mutex);
 		return -EINVAL;
 	}
 
 	ret = gbaudio_init_jack(module, comp->card);
 	if (ret) {
-		up_write(&card->controls_rwsem);
+		mutex_unlock(&gbcodec->register_mutex);
 		return ret;
 	}
 
@@ -867,7 +865,7 @@ int gbaudio_register_module(struct gbaudio_module_info *module)
 		ret = snd_soc_dapm_new_widgets(comp->card);
 	dev_dbg(comp->dev, "Registered %s module\n", module->name);
 
-	up_write(&card->controls_rwsem);
+	mutex_unlock(&gbcodec->register_mutex);
 	return ret;
 }
 EXPORT_SYMBOL(gbaudio_register_module);
@@ -935,13 +933,12 @@ static void gbaudio_codec_cleanup(struct gbaudio_module_info *module)
 void gbaudio_unregister_module(struct gbaudio_module_info *module)
 {
 	struct snd_soc_component *comp = gbcodec->component;
-	struct snd_card *card = comp->card->snd_card;
 	struct gbaudio_jack *jack, *n;
 	int mask;
 
 	dev_dbg(comp->dev, "Unregister %s module\n", module->name);
 
-	down_write(&card->controls_rwsem);
+	mutex_lock(&gbcodec->register_mutex);
 	mutex_lock(&gbcodec->lock);
 	gbaudio_codec_cleanup(module);
 	list_del(&module->list);
@@ -978,10 +975,8 @@ void gbaudio_unregister_module(struct gbaudio_module_info *module)
 		dev_dbg(comp->dev, "Removing %d controls\n",
 			module->num_controls);
 		/* release control semaphore */
-		up_write(&card->controls_rwsem);
 		gbaudio_remove_component_controls(comp, module->controls,
 						  module->num_controls);
-		down_write(&card->controls_rwsem);
 	}
 	if (module->dapm_widgets) {
 		dev_dbg(comp->dev, "Removing %d widgets\n",
@@ -992,7 +987,7 @@ void gbaudio_unregister_module(struct gbaudio_module_info *module)
 
 	dev_dbg(comp->dev, "Unregistered %s module\n", module->name);
 
-	up_write(&card->controls_rwsem);
+	mutex_unlock(&gbcodec->register_mutex);
 }
 EXPORT_SYMBOL(gbaudio_unregister_module);
 
@@ -1012,6 +1007,7 @@ static int gbcodec_probe(struct snd_soc_component *comp)
 	info->dev = comp->dev;
 	INIT_LIST_HEAD(&info->module_list);
 	mutex_init(&info->lock);
+	mutex_init(&info->register_mutex);
 	INIT_LIST_HEAD(&info->dai_list);
 
 	/* init dai_list used to maintain runtime stream info */

drivers/staging/greybus/audio_codec.h

@@ -71,6 +71,7 @@ struct gbaudio_codec_info {
 	/* to maintain runtime stream params for each DAI */
 	struct list_head dai_list;
 	struct mutex lock;
+	struct mutex register_mutex;
 };
 
 struct gbaudio_widget {