ALSA: core: Unify card allocation and free with and without devres

We implemented devres for allocating and releasing the card memory
itself, but this can be problematic when the delayed kobj release is
used.  Above all, the conditional kfree() is rather error-prone.

This patch changes the mechanism for snd_devm_card_new().  Now it
allocates a devres pointer for the card object that stores the result
of snd_card_new().  In return, at devres release, it unreferences the
card_dev refcount, so that we can use card_dev's release as the sole
point for releasing the memory at the very last.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/init.c

diff --git a/sound/core/init.c b/sound/core/init.c
index 5de6279..51e5243 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -149,10 +149,7 @@ static const struct attribute_group card_dev_attr_group;
 
 static void release_card_device(struct device *dev)
 {
-	struct snd_card *card = dev_to_snd_card(dev);
-
-	if (!card->managed)
-		kfree(card);
+	kfree(dev_to_snd_card(dev));
 }
 
 /**
@@ -196,9 +193,15 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
 }
 EXPORT_SYMBOL(snd_card_new);
 
+/* devres release for snd_devm_card_new() */
 static void __snd_card_release(struct device *dev, void *data)
 {
-	snd_card_free(data);
+	struct snd_card *card = *(struct snd_card **)data;
+
+	if (!card)
+		return;
+	snd_card_free(card);
+	put_device(&card->card_dev);
 }
 
 /**
@@ -231,21 +234,21 @@ int snd_devm_card_new(struct device *parent, int idx, const char *xid,
 		      struct snd_card **card_ret)
 {
 	struct snd_card *card;
+	struct snd_card **card_devres;
 	int err;
 
 	*card_ret = NULL;
-	card = devres_alloc(__snd_card_release, sizeof(*card) + extra_size,
-			    GFP_KERNEL);
-	if (!card)
+	card_devres = devres_alloc(__snd_card_release, sizeof(void *), GFP_KERNEL);
+	if (!card_devres)
 		return -ENOMEM;
-	card->managed = true;
-	err = snd_card_init(card, parent, idx, xid, module, extra_size);
-	if (err < 0) {
-		devres_free(card); /* in managed mode, we need to free manually */
-		return err;
-	}
+	devres_add(parent, card_devres);
 
-	devres_add(parent, card);
+	err = snd_card_new(parent, idx, xid, module, extra_size, &card);
+	if (err < 0)
+		return err;
+	card->managed = true;
+	get_device(&card->card_dev);
+	*card_devres = card;
 	*card_ret = card;
 	return 0;
 }
@@ -305,8 +308,7 @@ static int snd_card_init(struct snd_card *card, struct device *parent,
 		mutex_unlock(&snd_card_mutex);
 		dev_err(parent, "cannot find the slot for index %d (range 0-%i), error: %d\n",
 			 idx, snd_ecards_limit - 1, err);
-		if (!card->managed)
-			kfree(card); /* manually free here, as no destructor called */
+		kfree(card); /* manually free here, as no destructor called */
 		return err;
 	}
 	set_bit(idx, snd_cards_lock);		/* lock it */