At Wed, 3 Jun 2009 20:43:29 +0100,
Mark Brown wrote:
>
> 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.
Oh, thanks for catching this. Obviously I haven't tested the
latest code enough...
> 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.
Agreed, there can be a cleaner solution but your fix is definitely
safe. So I applied it as a quick fix.
Takashi
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
> ---
>
> This patch isn't terribly nice but I figured it was a more useful report
> than just the deadlock.
>
> sound/core/init.c | 31 +++++++++++++++++++------------
> 1 files changed, 19 insertions(+), 12 deletions(-)
>
> diff --git a/sound/core/init.c b/sound/core/init.c
> index 6557dd8..a578d05 100644
> --- 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);
> --
> 1.6.3.1
>
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