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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Andreas Pape <apape@de.adit-jv.com>,
        Eugeniu Rosca <erosca@de.adit-jv.com>,
        Takashi Iwai <tiwai@suse.de>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 103/229] ALSA: dmaengine: increment buffer pointer atomically
Date:   Mon, 24 Oct 2022 13:30:22 +0200
Message-Id: <20221024113002.353044201@linuxfoundation.org>
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From: Andreas Pape <apape@de.adit-jv.com>

[ Upstream commit d1c442019594692c64a70a86ad88eb5b6db92216 ]

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: e7f73a1613567a ("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 | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
index 8eb58c709b14..6f6da1128edc 100644
--- a/sound/core/pcm_dmaengine.c
+++ b/sound/core/pcm_dmaengine.c
@@ -139,12 +139,14 @@ 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);
-	if (prtd->pos >= snd_pcm_lib_buffer_bytes(substream))
-		prtd->pos = 0;
+	new_pos = prtd->pos + snd_pcm_lib_period_bytes(substream);
+	if (new_pos >= snd_pcm_lib_buffer_bytes(substream))
+		new_pos = 0;
+	prtd->pos = new_pos;
 
 	snd_pcm_period_elapsed(substream);
 }
-- 
2.35.1