serial: altera_uart: fix locking in polling mode

Since altera_uart_interrupt() may also be called from
a poll timer in "serving_softirq" context, use
spin_[lock_irqsave|unlock_irqrestore] variants, which
are appropriate for both softirq and hardware interrupt
contexts.

Fixes: 2f8b9c1 ("altera_uart: Add support for polling mode (IRQ-less)")
Signed-off-by: Gabriel Somlo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: gsomlo

drivers/tty/serial/altera_uart.c

@@ -259,16 +259,17 @@ static irqreturn_t altera_uart_interrupt(int irq, void *data)
 {
 	struct uart_port *port = data;
 	struct altera_uart *pp = container_of(port, struct altera_uart, port);
+	unsigned long flags;
 	unsigned int isr;
 
 	isr = altera_uart_readl(port, ALTERA_UART_STATUS_REG) & pp->imr;
 
-	spin_lock(&port->lock);
+	spin_lock_irqsave(&port->lock, flags);
 	if (isr & ALTERA_UART_STATUS_RRDY_MSK)
 		altera_uart_rx_chars(port);
 	if (isr & ALTERA_UART_STATUS_TRDY_MSK)
 		altera_uart_tx_chars(port);
-	spin_unlock(&port->lock);
+	spin_unlock_irqrestore(&port->lock, flags);
 
 	return IRQ_RETVAL(isr);
 }