linux-kernel - [PATCH 1/3] serial: qcom-geni: fix hard lockup on buffer flush

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Date: Mon, 24 Jun 2024 15:31:33 +0200
From: Johan Hovold <johan+linaro@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>
Cc: Konrad Dybcio <konrad.dybcio@...aro.org>,
	Douglas Anderson <dianders@...omium.org>,
	Bjorn Andersson <andersson@...nel.org>,
	linux-arm-msm@...r.kernel.org,
	linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Johan Hovold <johan+linaro@...nel.org>
Subject: [PATCH 1/3] serial: qcom-geni: fix hard lockup on buffer flush

The Qualcomm GENI serial driver does not handle buffer flushing and used
to print garbage characters when the circular buffer was cleared. Since
commit 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") this
instead results in a lockup due to qcom_geni_serial_send_chunk_fifo()
spinning indefinitely in the interrupt handler.

This is easily triggered by interrupting a command such as dmesg in a
serial console but can also happen when stopping a serial getty on
reboot.

Fix the immediate issue by printing NUL characters until the current TX
command has been completed.

Fixes: 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo")
Reported-by: Douglas Anderson <dianders@...omium.org>
Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
---
 drivers/tty/serial/qcom_geni_serial.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 2bd25afe0d92..1d5d6045879a 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -862,7 +862,7 @@ static void qcom_geni_serial_send_chunk_fifo(struct uart_port *uport,
 		memset(buf, 0, sizeof(buf));
 		tx_bytes = min(remaining, BYTES_PER_FIFO_WORD);
 
-		tx_bytes = uart_fifo_out(uport, buf, tx_bytes);
+		uart_fifo_out(uport, buf, tx_bytes);
 
 		iowrite32_rep(uport->membase + SE_GENI_TX_FIFOn, buf, 1);
 
-- 
2.44.1