[PATCH v2 2/3] serial: amba-pl011: cancel RS485 hrtimers after freeing IRQ

[Fan Wu]

The RS485 trigger hrtimers are embedded in the devm-managed port and can
fire after it is freed. The IRQ handler can arm a timer, so free the IRQ
first and then cancel both timers.

Complete the RS485 stop without arming a timer, and cancel the timers
in remove() for the suspend-then-unbind path, where shutdown is not
called.

This issue was found by an in-house static analysis tool.

Fixes: 2c1fd53af21b ("serial: amba-pl011: Fix RTS handling in RS485 mode")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <fanwu01@xxxxxxxxxx>
---
 drivers/tty/serial/amba-pl011.c | 52 ++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 17 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index b212e2bcd41a..e686835d5150 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1269,11 +1269,30 @@ static inline bool pl011_dma_rx_running(struct uart_amba_port *uap)
 #define pl011_dma_flush_buffer	NULL
 #endif
 
-static void pl011_rs485_tx_stop(struct uart_amba_port *uap)
+static void pl011_rs485_tx_stop_now(struct uart_amba_port *uap)
 {
 	struct uart_port *port = &uap->port;
 	u32 cr;
 
+	cr = pl011_read(uap, REG_CR);
+
+	if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
+		cr &= ~UART011_CR_RTS;
+	else
+		cr |= UART011_CR_RTS;
+
+	/* Disable the transmitter and reenable the transceiver */
+	cr &= ~UART011_CR_TXE;
+	cr |= UART011_CR_RXE;
+	pl011_write(cr, uap, REG_CR);
+
+	uap->rs485_tx_state = OFF;
+}
+
+static void pl011_rs485_tx_stop(struct uart_amba_port *uap)
+{
+	struct uart_port *port = &uap->port;
+
 	if (uap->rs485_tx_state == SEND)
 		uap->rs485_tx_state = WAIT_AFTER_SEND;
 
@@ -1297,19 +1316,7 @@ static void pl011_rs485_tx_stop(struct uart_amba_port *uap)
 		hrtimer_try_to_cancel(&uap->trigger_start_tx);
 	}
 
-	cr = pl011_read(uap, REG_CR);
-
-	if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
-		cr &= ~UART011_CR_RTS;
-	else
-		cr |= UART011_CR_RTS;
-
-	/* Disable the transmitter and reenable the transceiver */
-	cr &= ~UART011_CR_TXE;
-	cr |= UART011_CR_RXE;
-	pl011_write(cr, uap, REG_CR);
-
-	uap->rs485_tx_state = OFF;
+	pl011_rs485_tx_stop_now(uap);
 }
 
 static void pl011_stop_tx(struct uart_port *port)
@@ -2019,11 +2026,20 @@ static void pl011_shutdown(struct uart_port *port)
 
 	pl011_dma_shutdown(uap);
 
-	if ((port->rs485.flags & SER_RS485_ENABLED && uap->rs485_tx_state != OFF))
-		pl011_rs485_tx_stop(uap);
-
 	free_irq(uap->port.irq, uap);
 
+	/*
+	 * free_irq() drains the UART interrupt handler, which can arm either
+	 * timer.  Cancel the timers afterwards to drain their callbacks too.
+	 */
+	hrtimer_cancel(&uap->trigger_start_tx);
+	hrtimer_cancel(&uap->trigger_stop_tx);
+
+	uart_port_lock_irq(port);
+	if (uap->rs485_tx_state != OFF)
+		pl011_rs485_tx_stop_now(uap);
+	uart_port_unlock_irq(port);
+
 	pl011_disable_uart(uap);
 
 	/*
@@ -2941,6 +2957,8 @@ static void pl011_remove(struct amba_device *dev)
 	struct uart_amba_port *uap = amba_get_drvdata(dev);
 
 	uart_remove_one_port(&amba_reg, &uap->port);
+	hrtimer_cancel(&uap->trigger_start_tx);
+	hrtimer_cancel(&uap->trigger_stop_tx);
 	pl011_unregister_port(uap);
 }
 
-- 
2.34.1