[PATCH v2 18/21] ASoC: codecs: rt5677-spi: Free the DSP context on component remove

[Chancel Liu <chancel.liu@oss.nxp.com>]

From: Chancel Liu <chancel.liu@nxp.com>

component->dev is the underlying SPI bus device, whose devres lifetime
follows the physical devices probe/remove rather than the ASoC cards
bind/unbind. The rt5677_dsp context allocated in the component probe with
devm_kzalloc(component->dev, ...) therefore leaks on every card
bind/unbind cycle, and the delayed work initialised there is never
cancelled on unbind.

Allocate the context with kzalloc() and add a component .remove callback
that cancels the copy work, destroys the mutex and frees the context.

The exported rt5677_spi_hotword_detected(), called from the rt5677 codec
interrupt path, fetches the context via dev_get_drvdata(&g_spi->dev) and
dereferences it. Freeing the context on remove would let that callback
run concurrently and touch freed memory. Add a dsp_lock that serializes
the fetch/use in rt5677_spi_hotword_detected() against clearing the
drvdata in the remove callback, so once remove has cleared the pointer
the callback either observes NULL and bails out or has already finished.

Signed-off-by: Chancel Liu <chancel.liu@nxp.com>
---
 sound/soc/codecs/rt5677-spi.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/sound/soc/codecs/rt5677-spi.c b/sound/soc/codecs/rt5677-spi.c
index ebc527115ea5..0b2166082437 100644
--- a/sound/soc/codecs/rt5677-spi.c
+++ b/sound/soc/codecs/rt5677-spi.c
@@ -58,6 +58,8 @@
 
 static struct spi_device *g_spi;
 static DEFINE_MUTEX(spi_mutex);
+/* Serializes access to the DSP context against the exported hotword callback */
+static DEFINE_MUTEX(dsp_lock);
 
 struct rt5677_dsp {
 	struct device *dev;
@@ -380,8 +382,7 @@ static int rt5677_spi_pcm_probe(struct snd_soc_component *component)
 {
 	struct rt5677_dsp *rt5677_dsp;
 
-	rt5677_dsp = devm_kzalloc(component->dev, sizeof(*rt5677_dsp),
-			GFP_KERNEL);
+	rt5677_dsp = kzalloc_obj(*rt5677_dsp);
 	if (!rt5677_dsp)
 		return -ENOMEM;
 	rt5677_dsp->dev = &g_spi->dev;
@@ -392,9 +393,23 @@ static int rt5677_spi_pcm_probe(struct snd_soc_component *component)
 	return 0;
 }
 
+static void rt5677_spi_pcm_remove(struct snd_soc_component *component)
+{
+	struct rt5677_dsp *rt5677_dsp =
+			snd_soc_component_get_drvdata(component);
+
+	scoped_guard(mutex, &dsp_lock)
+		snd_soc_component_set_drvdata(component, NULL);
+
+	cancel_delayed_work_sync(&rt5677_dsp->copy_work);
+	mutex_destroy(&rt5677_dsp->dma_lock);
+	kfree(rt5677_dsp);
+}
+
 static const struct snd_soc_component_driver rt5677_spi_dai_component = {
 	.name			= DRV_NAME,
 	.probe			= rt5677_spi_pcm_probe,
+	.remove			= rt5677_spi_pcm_remove,
 	.open			= rt5677_spi_pcm_open,
 	.close			= rt5677_spi_pcm_close,
 	.hw_params		= rt5677_spi_hw_params,
@@ -579,6 +594,8 @@ void rt5677_spi_hotword_detected(void)
 	if (!g_spi)
 		return;
 
+	guard(mutex)(&dsp_lock);
+
 	rt5677_dsp = dev_get_drvdata(&g_spi->dev);
 	if (!rt5677_dsp) {
 		dev_err(&g_spi->dev, "Can't get rt5677_dsp\n");
-- 
2.50.1