[PATCH] Fix a potential issue in mpc52xx uart driver

[Andrew Liu <shengping.liu@windriver.com>]

mpc52xx_uart_int and __uart_put_char both try to acquire the
port->lock. Therefore the function sequence of:

mpc52xx_uart_int--> ...-->flush_to_ldisc-->...-->__uart_put_char

can potentially trigger a deadlock. To avoid this deadlock a fix
similar to that found in the 8250.c serial driver is applied. The
deadlock is avoided by releasing the lock before pushing a buffer
and reacquiring it when completed.

Signed-off-by: Andrew Liu <shengping.liu@windriver.com>

diff --git a/drivers/serial/mpc52xx_uart.c b/drivers/serial/mpc52xx_uart.c
index d93b357..5f95e53 100644
--- a/drivers/serial/mpc52xx_uart.c
+++ b/drivers/serial/mpc52xx_uart.c
@@ -783,7 +783,9 @@ mpc52xx_uart_int_rx_chars(struct uart_port *port)
                 }
         }

+       spin_unlock(&port->lock);
         tty_flip_buffer_push(tty);
+       spin_lock(&port->lock);

         return psc_ops->raw_rx_rdy(port);
  }