[alsa-devel] [PATCH] ASoC: core: move DAI pre-links initiation to snd_soc_instantiate_card

[Tzung-Bi Shih]

Kernel crashes when an ASoC component rebinding.

As an example, by using the following commands:
- echo -n max98357a > /sys/bus/platform/drivers/max98357a/unbind
- echo -n max98357a > /sys/bus/platform/drivers/max98357a/bind

Got the error message:
"Unable to handle kernel NULL pointer dereference at virtual address".

The call trace:
snd_soc_is_matching_component+0x30/0x6c
soc_bind_dai_link+0x16c/0x240
snd_soc_bind_card+0x1e4/0xb10
snd_soc_add_component+0x270/0x300
snd_soc_register_component+0x54/0x6c
devm_snd_soc_register_component+0x68/0xac
max98357a_platform_probe+0x7c/0x94

The dai_link->platforms has been reset to NULL by soc_cleanup_platform()
in soc_cleanup_card_resources() when un-registering component.  However,
it has no chance to re-allocate the dai_link->platforms when registering
the component again.

Move the DAI pre-links initiation from snd_soc_register_card() to
snd_soc_instantiate_card() to make sure all DAI pre-links get initiated
when component rebinding.

Signed-off-by: Tzung-Bi Shih <tzungbi at google.com>
---
 sound/soc/soc-core.c | 28 ++++++++++------------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index 2d3520fca613..82ff384753c7 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -2072,6 +2072,15 @@ static int snd_soc_instantiate_card(struct snd_soc_card *card)
 	mutex_lock(&client_mutex);
 	mutex_lock_nested(&card->mutex, SND_SOC_CARD_CLASS_INIT);
 
+	for_each_card_prelinks(card, i, dai_link) {
+		ret = soc_init_dai_link(card, dai_link);
+		if (ret) {
+			dev_err(card->dev, "ASoC: failed to init link %s: %d\n",
+				dai_link->name, ret);
+			goto probe_end;
+		}
+	}
+
 	card->dapm.bias_level = SND_SOC_BIAS_OFF;
 	card->dapm.dev = card->dev;
 	card->dapm.card = card;
@@ -2241,7 +2250,7 @@ static int snd_soc_instantiate_card(struct snd_soc_card *card)
 	snd_soc_dapm_sync(&card->dapm);
 
 probe_end:
-	if (ret < 0)
+	if (ret < 0 && ret != -EPROBE_DEFER)
 		soc_cleanup_card_resources(card);
 
 	mutex_unlock(&card->mutex);
@@ -2794,26 +2803,9 @@ static int snd_soc_bind_card(struct snd_soc_card *card)
  */
 int snd_soc_register_card(struct snd_soc_card *card)
 {
-	int i, ret;
-	struct snd_soc_dai_link *link;
-
 	if (!card->name || !card->dev)
 		return -EINVAL;
 
-	mutex_lock(&client_mutex);
-	for_each_card_prelinks(card, i, link) {
-
-		ret = soc_init_dai_link(card, link);
-		if (ret) {
-			soc_cleanup_platform(card);
-			dev_err(card->dev, "ASoC: failed to init link %s\n",
-				link->name);
-			mutex_unlock(&client_mutex);
-			return ret;
-		}
-	}
-	mutex_unlock(&client_mutex);
-
 	dev_set_drvdata(card->dev, card);
 
 	snd_soc_initialize_card_lists(card);
-- 
2.22.0.rc1.257.g3120a18244-goog