Patch "serial: 8250: lock port for UART_IER access in omap8250_irq()" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     serial-8250-lock-port-for-uart_ier-access-in-omap825.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a299b95389eec3c6825b6c80819f8f529cbe28a4
Author: John Ogness <john.ogness@xxxxxxxxxxxxx>
Date:   Thu May 25 11:37:58 2023 +0206

    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@xxxxxxxxxxxxx>
    Reviewed-by: Tony Lindgren <tony@xxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230525093159.223817-8-john.ogness@xxxxxxxxxxxxx
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 28e243312286f..de0447c87846b 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -653,17 +653,18 @@ 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);