ASoC: stm32: sai: fix race condition in irq handler

When snd_pcm_stop_xrun() is called in interrupt routine,
substream context may have already been released.
Add protection on substream context.
Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/stm/stm32_sai_sub.c

@@ -102,6 +102,7 @@
  * @spdif_frm_cnt: S/PDIF playback frame counter
  * @iec958: iec958 data
  * @ctrl_lock: control lock
+ * @irq_lock: prevent race condition with IRQ
  */
 struct stm32_sai_sub_data {
 	struct platform_device *pdev;
@@ -133,6 +134,7 @@ struct stm32_sai_sub_data {
 	unsigned int spdif_frm_cnt;
 	struct snd_aes_iec958 iec958;
 	struct mutex ctrl_lock; /* protect resources accessed by controls */
+	spinlock_t irq_lock; /* used to prevent race condition with IRQ */
 };
 
 enum stm32_sai_fifo_th {
@@ -474,8 +476,10 @@ static irqreturn_t stm32_sai_isr(int irq, void *devid)
 		status = SNDRV_PCM_STATE_XRUN;
 	}
 
-	if (status != SNDRV_PCM_STATE_RUNNING)
+	spin_lock(&sai->irq_lock);
+	if (status != SNDRV_PCM_STATE_RUNNING && sai->substream)
 		snd_pcm_stop_xrun(sai->substream);
+	spin_unlock(&sai->irq_lock);
 
 	return IRQ_HANDLED;
 }
@@ -679,8 +683,11 @@ static int stm32_sai_startup(struct snd_pcm_substream *substream,
 {
 	struct stm32_sai_sub_data *sai = snd_soc_dai_get_drvdata(cpu_dai);
 	int imr, cr2, ret;
+	unsigned long flags;
 
+	spin_lock_irqsave(&sai->irq_lock, flags);
 	sai->substream = substream;
+	spin_unlock_irqrestore(&sai->irq_lock, flags);
 
 	if (STM_SAI_PROTOCOL_IS_SPDIF(sai)) {
 		snd_pcm_hw_constraint_mask64(substream->runtime,
@@ -1059,6 +1066,7 @@ static void stm32_sai_shutdown(struct snd_pcm_substream *substream,
 			       struct snd_soc_dai *cpu_dai)
 {
 	struct stm32_sai_sub_data *sai = snd_soc_dai_get_drvdata(cpu_dai);
+	unsigned long flags;
 
 	regmap_update_bits(sai->regmap, STM_SAI_IMR_REGX, SAI_XIMR_MASK, 0);
 
@@ -1069,7 +1077,9 @@ static void stm32_sai_shutdown(struct snd_pcm_substream *substream,
 
 	clk_rate_exclusive_put(sai->sai_mclk);
 
+	spin_lock_irqsave(&sai->irq_lock, flags);
 	sai->substream = NULL;
+	spin_unlock_irqrestore(&sai->irq_lock, flags);
 }
 
 static int stm32_sai_pcm_new(struct snd_soc_pcm_runtime *rtd,
@@ -1433,6 +1443,7 @@ static int stm32_sai_sub_probe(struct platform_device *pdev)
 
 	sai->pdev = pdev;
 	mutex_init(&sai->ctrl_lock);
+	spin_lock_init(&sai->irq_lock);
 	platform_set_drvdata(pdev, sai);
 
 	sai->pdata = dev_get_drvdata(pdev->dev.parent);