ASoC: soc-card: Fix missing locking in snd_soc_card_get_kcontrol()

snd_soc_card_get_kcontrol() must be holding a read lock on
card->controls_rwsem while walking the controls list.

Compare with snd_ctl_find_numid().

The existing function is renamed snd_soc_card_get_kcontrol_locked()
so that it can be called from contexts that are already holding
card->controls_rwsem (for example, control get/put functions).

There are few direct or indirect callers of
snd_soc_card_get_kcontrol(), and most are safe. Three require
changes, which have been included in this patch:

codecs/cs35l45.c:
  cs35l45_activate_ctl() is called from a control put() function so
  is changed to call snd_soc_card_get_kcontrol_locked().

codecs/cs35l56.c:
  cs35l56_sync_asp1_mixer_widgets_with_firmware() is called from
  control get()/put() functions so is changed to call
  snd_soc_card_get_kcontrol_locked().

fsl/fsl_xcvr.c:
  fsl_xcvr_activate_ctl() is called from three places, one of which
  already holds card->controls_rwsem:
  1. fsl_xcvr_mode_put(), a control put function, which will
     already be holding card->controls_rwsem.
  2. fsl_xcvr_startup(), a DAI startup function.
  3. fsl_xcvr_shutdown(), a DAI shutdown function.

  To fix this, fsl_xcvr_activate_ctl() has been changed to call
  snd_soc_card_get_kcontrol_locked() so that it is safe to call
  directly from fsl_xcvr_mode_put().
  The fsl_xcvr_startup() and fsl_xcvr_shutdown() functions have been
  changed to take a read lock on card->controls_rsem() around calls
  to fsl_xcvr_activate_ctl(). While this is not very elegant, it
  keeps the change small, to avoid this patch creating a large
  collateral churn in fsl/fsl_xcvr.c.

Analysis of other callers of snd_soc_card_get_kcontrol() is that
they do not need any changes, they are not holding card->controls_rwsem
when they call snd_soc_card_get_kcontrol().

Direct callers of snd_soc_card_get_kcontrol():
  fsl/fsl_spdif.c: fsl_spdif_dai_probe() - DAI probe function
  fsl/fsl_micfil.c: voice_detected_fn() - IRQ handler

Indirect callers via soc_component_notify_control():
  codecs/cs42l43: cs42l43_mic_shutter() - IRQ handler
  codecs/cs42l43: cs42l43_spk_shutter() - IRQ handler
  codecs/ak4118.c: ak4118_irq_handler() - IRQ handler
  codecs/wm_adsp.c: wm_adsp_write_ctl() - not currently used

Indirect callers via snd_soc_limit_volume():
  qcom/sc8280xp.c: sc8280xp_snd_init() - DAIlink init function
  ti/rx51.c: rx51_aic34_init() - DAI init function

I don't have hardware to test the fsl/*, qcom/sc828xp.c, ti/rx51.c
and ak4118.c changes.

Backport note:
The fsl/, qcom/, cs35l45, cs35l56 and cs42l43 callers were added
since the Fixes commit so won't all be present on older kernels.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: 209c6cdfd283 ("ASoC: soc-card: move snd_soc_card_get_kcontrol() to soc-card")
Link: https://lore.kernel.org/r/20240221123710.690224-1-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 22 insertions, 2 deletions

diff --git a/sound/soc/soc-card.c b/sound/soc/soc-card.c
index 285ab4c9c716..8a2f163da6bc 100644
--- a/sound/soc/soc-card.c
+++ b/sound/soc/soc-card.c
@@ -5,6 +5,9 @@
 // Copyright (C) 2019 Renesas Electronics Corp.
 // Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
 //
+
+#include <linux/lockdep.h>
+#include <linux/rwsem.h>
 #include <sound/soc.h>
 #include <sound/jack.h>
 
@@ -26,12 +29,15 @@ static inline int _soc_card_ret(struct snd_soc_card *card,
 	return ret;
 }
 
-struct snd_kcontrol *snd_soc_card_get_kcontrol(struct snd_soc_card *soc_card,
-					       const char *name)
+struct snd_kcontrol *snd_soc_card_get_kcontrol_locked(struct snd_soc_card *soc_card,
+						      const char *name)
 {
 	struct snd_card *card = soc_card->snd_card;
 	struct snd_kcontrol *kctl;
 
+	/* must be held read or write */
+	lockdep_assert_held(&card->controls_rwsem);
+
 	if (unlikely(!name))
 		return NULL;
 
@@ -40,6 +46,20 @@ struct snd_kcontrol *snd_soc_card_get_kcontrol(struct snd_soc_card *soc_card,
 			return kctl;
 	return NULL;
 }
+EXPORT_SYMBOL_GPL(snd_soc_card_get_kcontrol_locked);
+
+struct snd_kcontrol *snd_soc_card_get_kcontrol(struct snd_soc_card *soc_card,
+					       const char *name)
+{
+	struct snd_card *card = soc_card->snd_card;
+	struct snd_kcontrol *kctl;
+
+	down_read(&card->controls_rwsem);
+	kctl = snd_soc_card_get_kcontrol_locked(soc_card, name);
+	up_read(&card->controls_rwsem);
+
+	return kctl;
+}
 EXPORT_SYMBOL_GPL(snd_soc_card_get_kcontrol);
 
 static int jack_new(struct snd_soc_card *card, const char *id, int type,