ALSA: Add a reference counter to card instance

For more strict protection for wild disconnections, a refcount is
introduced to the card instance, and let it up/down when an object is
referred via snd_lookup_*() in the open ops.

The free-after-last-close check is also changed to check this refcount
instead of the empty list, too.

Reported-by: Matthieu CASTET <matthieu.castet@parrot.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 30 insertions, 20 deletions

diff --git a/sound/core/init.c b/sound/core/init.c
index d8ec849..7b012d1 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -213,6 +213,7 @@ int snd_card_create(int idx, const char *xid,
 	spin_lock_init(&card->files_lock);
 	INIT_LIST_HEAD(&card->files_list);
 	init_waitqueue_head(&card->shutdown_sleep);
+	atomic_set(&card->refcount, 0);
 #ifdef CONFIG_PM
 	mutex_init(&card->power_lock);
 	init_waitqueue_head(&card->power_sleep);
@@ -446,21 +447,36 @@ static int snd_card_do_free(struct snd_card *card)
 	return 0;
 }
 
+/**
+ * snd_card_unref - release the reference counter
+ * @card: the card instance
+ *
+ * Decrements the reference counter.  When it reaches to zero, wake up
+ * the sleeper and call the destructor if needed.
+ */
+void snd_card_unref(struct snd_card *card)
+{
+	if (atomic_dec_and_test(&card->refcount)) {
+		wake_up(&card->shutdown_sleep);
+		if (card->free_on_last_close)
+			snd_card_do_free(card);
+	}
+}
+EXPORT_SYMBOL(snd_card_unref);
+
 int snd_card_free_when_closed(struct snd_card *card)
 {
-	int free_now = 0;
-	int ret = snd_card_disconnect(card);
-	if (ret)
-		return ret;
+	int ret;
 
-	spin_lock(&card->files_lock);
-	if (list_empty(&card->files_list))
-		free_now = 1;
-	else
-		card->free_on_last_close = 1;
-	spin_unlock(&card->files_lock);
+	atomic_inc(&card->refcount);
+	ret = snd_card_disconnect(card);
+	if (ret) {
+		atomic_dec(&card->refcount);
+		return ret;
+	}
 
-	if (free_now)
+	card->free_on_last_close = 1;
+	if (atomic_dec_and_test(&card->refcount))
 		snd_card_do_free(card);
 	return 0;
 }
@@ -474,7 +490,7 @@ int snd_card_free(struct snd_card *card)
 		return ret;
 
 	/* wait, until all devices are ready for the free operation */
-	wait_event(card->shutdown_sleep, list_empty(&card->files_list));
+	wait_event(card->shutdown_sleep, !atomic_read(&card->refcount));
 	snd_card_do_free(card);
 	return 0;
 }
@@ -886,6 +902,7 @@ int snd_card_file_add(struct snd_card *card, struct file *file)
 		return -ENODEV;
 	}
 	list_add(&mfile->list, &card->files_list);
+	atomic_inc(&card->refcount);
 	spin_unlock(&card->files_lock);
 	return 0;
 }
@@ -908,7 +925,6 @@ EXPORT_SYMBOL(snd_card_file_add);
 int snd_card_file_remove(struct snd_card *card, struct file *file)
 {
 	struct snd_monitor_file *mfile, *found = NULL;
-	int last_close = 0;
 
 	spin_lock(&card->files_lock);
 	list_for_each_entry(mfile, &card->files_list, list) {
@@ -923,19 +939,13 @@ int snd_card_file_remove(struct snd_card *card, struct file *file)
 			break;
 		}
 	}
-	if (list_empty(&card->files_list))
-		last_close = 1;
 	spin_unlock(&card->files_lock);
-	if (last_close) {
-		wake_up(&card->shutdown_sleep);
-		if (card->free_on_last_close)
-			snd_card_do_free(card);
-	}
 	if (!found) {
 		snd_printk(KERN_ERR "ALSA card file remove problem (%p)\n", file);
 		return -ENOENT;
 	}
 	kfree(found);
+	snd_card_unref(card);
 	return 0;
 }