linux-kernel - [PATCH tty v1 7/8] serial: 8250: lock port for UART_IER access in omap8250

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Message-Id: <20230525093159.223817-8-john.ogness@linutronix.de>
Date:   Thu, 25 May 2023 11:37:58 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Jiri Slaby <jirislaby@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Tony Lindgren <tony@...mide.com>,
        Lukas Wunner <lukas@...ner.de>,
        Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        linux-serial@...r.kernel.org
Subject: [PATCH tty v1 7/8] serial: 8250: lock port for UART_IER access in omap8250_irq()

omap8250_irq() accesses UART_IER. This register is modified twice
by each console write (serial8250_console_write()) under the port
lock. omap8250_irq() must also take the port lock to guanentee
synchronized access to UART_IER.

Since the port lock is already being taken for the stop_rx() callback
and since it is safe to call cancel_delayed_work() while holding the
port lock, simply extend the port lock region to include UART_IER
access.

Fixes: 1fe0e1fa3209 ("serial: 8250_omap: Handle optional overrun-throttle-ms property")
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 drivers/tty/serial/8250/8250_omap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 34939462fd69..3225c95fde1d 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -659,17 +659,18 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)
 	if ((lsr & UART_LSR_OE) && up->overrun_backoff_time_ms > 0) {
 		unsigned long delay;
 
+		/* Synchronize UART_IER access against the console. */
+		spin_lock(&port->lock);
 		up->ier = port->serial_in(port, UART_IER);
 		if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) {
-			spin_lock(&port->lock);
 			port->ops->stop_rx(port);
-			spin_unlock(&port->lock);
 		} else {
 			/* Keep restarting the timer until
 			 * the input overrun subsides.
 			 */
 			cancel_delayed_work(&up->overrun_backoff);
 		}
+		spin_unlock(&port->lock);
 
 		delay = msecs_to_jiffies(up->overrun_backoff_time_ms);
 		schedule_delayed_work(&up->overrun_backoff, delay);
-- 
2.30.2