tty: serial: men_z135_uart.c: Fix race between IRQ and set_termios()

Fix panic caused by a race between men_z135_intr() and men_z135_set_termios().

men_z135_intr() and men_z135_set_termios() both hold the struct uart_port::lock
spinlock, but men_z135_intr() does a spin_lock_irqsave() and
men_z135_set_termios() does a normal spin_lock(), which can lead to a deadlock
when an interrupt is called while the lock is being helt by
men_z135_set_termios().

This was discovered using a insmod, hardware looppback send/receive, rmmod
stress test.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Cc: Andreas Werner <andreas.werner@men.de>
Cc: stable@vger.kernel.org # v4.0+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/men_z135_uart.c

@@ -392,7 +392,6 @@ static irqreturn_t men_z135_intr(int irq, void *data)
 	struct men_z135_port *uart = (struct men_z135_port *)data;
 	struct uart_port *port = &uart->port;
 	bool handled = false;
-	unsigned long flags;
 	int irq_id;
 
 	uart->stat_reg = ioread32(port->membase + MEN_Z135_STAT_REG);
@@ -401,7 +400,7 @@ static irqreturn_t men_z135_intr(int irq, void *data)
 	if (!irq_id)
 		goto out;
 
-	spin_lock_irqsave(&port->lock, flags);
+	spin_lock(&port->lock);
 	/* It's save to write to IIR[7:6] RXC[9:8] */
 	iowrite8(irq_id, port->membase + MEN_Z135_STAT_REG);
 
@@ -427,7 +426,7 @@ static irqreturn_t men_z135_intr(int irq, void *data)
 		handled = true;
 	}
 
-	spin_unlock_irqrestore(&port->lock, flags);
+	spin_unlock(&port->lock);
 out:
 	return IRQ_RETVAL(handled);
 }
@@ -717,7 +716,7 @@ static void men_z135_set_termios(struct uart_port *port,
 
 	baud = uart_get_baud_rate(port, termios, old, 0, uart_freq / 16);
 
-	spin_lock(&port->lock);
+	spin_lock_irq(&port->lock);
 	if (tty_termios_baud_rate(termios))
 		tty_termios_encode_baud_rate(termios, baud, baud);
 
@@ -725,7 +724,7 @@ static void men_z135_set_termios(struct uart_port *port,
 	iowrite32(bd_reg, port->membase + MEN_Z135_BAUD_REG);
 
 	uart_update_timeout(port, termios->c_cflag, baud);
-	spin_unlock(&port->lock);
+	spin_unlock_irq(&port->lock);
 }
 
 static const char *men_z135_type(struct uart_port *port)