serial: 8250: lock port for UART_IER access in omap8250_irq()

[ Upstream commit 25614735a647693c1260f253dc3ab32127697806 ]

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@linutronix.de>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20230525093159.223817-8-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 7ecd2d3..17a2302 100644 (file)
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -639,17 +639,18 @@ 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);