ALSA: dmaengine: increment buffer pointer atomically

[ Upstream commit d1c4420195 ]

Setting pointer and afterwards checking for wraparound leads
to the possibility of returning the inconsistent pointer position.

This patch increments buffer pointer atomically to avoid this issue.

Fixes: e7f73a1613 ("ASoC: Add dmaengine PCM helper functions")
Signed-off-by: Andreas Pape <apape@de.adit-jv.com>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Link: https://lore.kernel.org/r/1664211493-11789-1-git-send-email-erosca@de.adit-jv.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

sound/core/pcm_dmaengine.c

@@ -132,12 +132,14 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_set_config_from_dai_data);
 
 static void dmaengine_pcm_dma_complete(void *arg)
 {
+	unsigned int new_pos;
 	struct snd_pcm_substream *substream = arg;
 	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
 
-	prtd->pos += snd_pcm_lib_period_bytes(substream);
+	new_pos = prtd->pos + snd_pcm_lib_period_bytes(substream);
-	if (prtd->pos >= snd_pcm_lib_buffer_bytes(substream))
+	if (new_pos >= snd_pcm_lib_buffer_bytes(substream))
-		prtd->pos = 0;
+		new_pos = 0;
+	prtd->pos = new_pos;
 
 	snd_pcm_period_elapsed(substream);
 }