releases/6.12.58/alsa-serial-generic-remove-shared-static-buffer.patch

From 01c961b9730b780c9689a480cf995b8b5238a88d Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 15 Sep 2025 10:42:19 +0100
Subject: ALSA: serial-generic: remove shared static buffer

From: John Keeping <jkeeping@inmusicbrands.com>

[ Upstream commit 84973249011fda3ff292f83439a062fec81ef982 ]

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@inmusicbrands.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 36409a56c675e..d0e2e656c31c1 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