linux-kernel - [PATCH] serial: mxs-auart: add spinlock around changing cts state

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Message-ID: <20240315154150.28391-1-emil.kronborg@protonmail.com>
Date: Fri, 15 Mar 2024 15:42:29 +0000
From: Emil Kronborg <emil.kronborg@...tonmail.com>
To: jirislaby@...nel.org, gregkh@...uxfoundation.org
Cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev, Emil Kronborg <emil.kronborg@...tonmail.com>
Subject: [PATCH] serial: mxs-auart: add spinlock around changing cts state

The uart_handle_cts_change() function in serial_core expects the caller
to hold uport->lock. For example, I have seen the below kernel splat,
when the Bluetooth driver is loaded on an i.MX28 board.

    [   85.119255] ------------[ cut here ]------------
    [   85.124413] WARNING: CPU: 0 PID: 27 at /drivers/tty/serial/serial_core.c:3453 uart_handle_cts_change+0xb4/0xec
    [   85.134694] Modules linked in: hci_uart bluetooth ecdh_generic ecc wlcore_sdio configfs
    [   85.143314] CPU: 0 PID: 27 Comm: kworker/u3:0 Not tainted 6.6.3-00021-gd62a2f068f92 #1
    [   85.151396] Hardware name: Freescale MXS (Device Tree)
    [   85.156679] Workqueue: hci0 hci_power_on [bluetooth]
    [   85.164243]  unwind_backtrace from show_stack+0x10/0x14
    (...)

Signed-off-by: Emil Kronborg <emil.kronborg@...tonmail.com>
---
 drivers/tty/serial/mxs-auart.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
index 4749331fe618..1e8853eae504 100644
--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c
@@ -1086,11 +1086,13 @@ static void mxs_auart_set_ldisc(struct uart_port *port,
 
 static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
 {
-	u32 istat;
+	u32 istat, stat;
 	struct mxs_auart_port *s = context;
 	u32 mctrl_temp = s->mctrl_prev;
-	u32 stat = mxs_read(s, REG_STAT);
 
+	uart_port_lock(&s->port);
+
+	stat = mxs_read(s, REG_STAT);
 	istat = mxs_read(s, REG_INTR);
 
 	/* ack irq */
@@ -1126,6 +1128,8 @@ static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
 		istat &= ~AUART_INTR_TXIS;
 	}
 
+	uart_port_unlock(&s->port);
+
 	return IRQ_HANDLED;
 }
 
-- 
2.44.0