ALSA: Fix double locking of card list in snd_card_register()

The introduction of snd_card_set_id() added a lock on the card list
to the old choose_default_id() function when using it to implement
the new API call. This lock is needed to allow us to walk the list
and check to see if our new name is a duplicate. Unfortunately this
causes a lockup when called from snd_card_register() (in cases
where no ID is supplied for the card) since the card list is already
locked there.

Fix this fairly hideously by factoring out the implementation and
using a flag to indicate if the lock should be held. A better fix
would probably be to refactor snd_card_register() to move the
_set_id() outside the locking region but I can't immediately see
anything I can convince myself is safe.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/init.c b/sound/core/init.c
index 6557dd8..a578d05 100644 (file)
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -476,15 +476,8 @@ int snd_card_free(struct snd_card *card)
 
 EXPORT_SYMBOL(snd_card_free);
 
-/**
- *  snd_card_set_id - set card identification name
- *  @card: soundcard structure
- *  @nid: new identification string
- *
- *  This function sets the card identification and checks for name
- *  collisions.
- */
-void snd_card_set_id(struct snd_card *card, const char *nid)
+static void snd_card_set_id_internal(struct snd_card *card, const char *nid,
+                                    int do_locking)
 {
        int i, len, idx_flag = 0, loops = SNDRV_CARDS;
        const char *spos, *src;
@@ -529,14 +522,16 @@ void snd_card_set_id(struct snd_card *card, const char *nid)
                }
                if (!snd_info_check_reserved_words(id))
                        goto __change;
-               mutex_lock(&snd_card_mutex);
+               if (do_locking)
+                       mutex_lock(&snd_card_mutex);
                for (i = 0; i < snd_ecards_limit; i++) {
                        if (snd_cards[i] && !strcmp(snd_cards[i]->id, id)) {
                                mutex_unlock(&snd_card_mutex);
                                goto __change;
                        }
                }
-               mutex_unlock(&snd_card_mutex);
+               if (do_locking)
+                       mutex_unlock(&snd_card_mutex);
                break;
 
              __change:
@@ -561,6 +556,18 @@ void snd_card_set_id(struct snd_card *card, const char *nid)
        }
 }
 
+/**
+ *  snd_card_set_id - set card identification name
+ *  @card: soundcard structure
+ *  @nid: new identification string
+ *
+ *  This function sets the card identification and checks for name
+ *  collisions.
+ */
+void snd_card_set_id(struct snd_card *card, const char *nid)
+{
+       snd_card_set_id_internal(card, nid, 1);
+}
 EXPORT_SYMBOL(snd_card_set_id);
 
 #ifndef CONFIG_SYSFS_DEPRECATED
@@ -657,7 +664,7 @@ int snd_card_register(struct snd_card *card)
                return 0;
        }
        if (card->id[0] == '\0')
-               snd_card_set_id(card, NULL);
+               snd_card_set_id_internal(card, NULL, 0);
        snd_cards[card->number] = card;
        mutex_unlock(&snd_card_mutex);
        init_info_for_card(card);