linux-kernel - [PATCH] ALSA: serial-generic: remove shared static buffer

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Message-ID: <20250915094220.2959202-1-jkeeping@inmusicbrands.com>
Date: Mon, 15 Sep 2025 10:42:19 +0100
From: John Keeping <jkeeping@...usicbrands.com>
To: linux-sound@...r.kernel.org
Cc: John Keeping <jkeeping@...usicbrands.com>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] ALSA: serial-generic: remove shared static buffer

If multiple instances of this driver are instantiated and try to send
concurrently then the single static buffer snd_serial_generic_tx_work()
will cause corruption in the data output.

Move the buffer into the per-instance driver data to avoid this.

Signed-off-by: John Keeping <jkeeping@...usicbrands.com>
---
 sound/drivers/serial-generic.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/sound/drivers/serial-generic.c b/sound/drivers/serial-generic.c
index 21ae053c05767..766206c6ca75a 100644
--- a/sound/drivers/serial-generic.c
+++ b/sound/drivers/serial-generic.c
@@ -37,6 +37,8 @@ MODULE_LICENSE("GPL");
 #define SERIAL_TX_STATE_ACTIVE	1
 #define SERIAL_TX_STATE_WAKEUP	2
 
+#define INTERNAL_BUF_SIZE 256
+
 struct snd_serial_generic {
 	struct serdev_device *serdev;
 
@@ -51,6 +53,7 @@ struct snd_serial_generic {
 	struct work_struct tx_work;
 	unsigned long tx_state;
 
+	char tx_buf[INTERNAL_BUF_SIZE];
 };
 
 static void snd_serial_generic_tx_wakeup(struct snd_serial_generic *drvdata)
@@ -61,11 +64,8 @@ static void snd_serial_generic_tx_wakeup(struct snd_serial_generic *drvdata)
 	schedule_work(&drvdata->tx_work);
 }
 
-#define INTERNAL_BUF_SIZE 256
-
 static void snd_serial_generic_tx_work(struct work_struct *work)
 {
-	static char buf[INTERNAL_BUF_SIZE];
 	int num_bytes;
 	struct snd_serial_generic *drvdata = container_of(work, struct snd_serial_generic,
 						   tx_work);
@@ -78,8 +78,10 @@ static void snd_serial_generic_tx_work(struct work_struct *work)
 		if (!test_bit(SERIAL_MODE_OUTPUT_OPEN, &drvdata->filemode))
 			break;
 
-		num_bytes = snd_rawmidi_transmit_peek(substream, buf, INTERNAL_BUF_SIZE);
-		num_bytes = serdev_device_write_buf(drvdata->serdev, buf, num_bytes);
+		num_bytes = snd_rawmidi_transmit_peek(substream, drvdata->tx_buf,
+						      INTERNAL_BUF_SIZE);
+		num_bytes = serdev_device_write_buf(drvdata->serdev, drvdata->tx_buf,
+						    num_bytes);
 
 		if (!num_bytes)
 			break;
-- 
2.51.0