serial: bfin-uart: avoid dead lock in rx irq handler in smp kernel

Disabing dma irq and lock bottom half in smp kernel doesn't ensure exclusive
uart access. Call spin_lock_irqsave() instead.
Signed-off-by: Steven Miao <realmz6@gmail.com>
Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/bfin_uart.c

@@ -477,9 +477,9 @@ static void bfin_serial_dma_rx_chars(struct bfin_serial_port *uart)
 void bfin_serial_rx_dma_timeout(struct bfin_serial_port *uart)
 {
 	int x_pos, pos;
+	unsigned long flags;
 
-	dma_disable_irq_nosync(uart->rx_dma_channel);
-	spin_lock_bh(&uart->rx_lock);
+	spin_lock_irqsave(&uart->rx_lock, flags);
 
 	/* 2D DMA RX buffer ring is used. Because curr_y_count and
 	 * curr_x_count can't be read as an atomic operation,
@@ -510,8 +510,7 @@ void bfin_serial_rx_dma_timeout(struct bfin_serial_port *uart)
 		uart->rx_dma_buf.tail = uart->rx_dma_buf.head;
 	}
 
-	spin_unlock_bh(&uart->rx_lock);
-	dma_enable_irq(uart->rx_dma_channel);
+	spin_unlock_irqrestore(&uart->rx_lock, flags);
 
 	mod_timer(&(uart->rx_dma_timer), jiffies + DMA_RX_FLUSH_JIFFIES);
 }