ENGR00154346 UART: fix uart deadlock

UART hold the following locks in order of:

imx_set_termios():
--> spin_lock_irqsave(&sport->port.lock, flags)
    del_timer_sync(&sport->timer);
	--> spin_lock(timer->base->lock);
    	--> spin_unlock(timer->base->lock);
    spin_unlock_irqrestore(&sport->port.lock);

while when imx_timeout() may invoked in following stack:
run_timer_softirq():
--> spin_lock_irqsave(timer->base->lock, flags);
    imx_timeout();
	--> spin_lock_irqsave(&sport->port.lock, flags);
	    ...;
	--> spin_unlock_irqrestore(&sport->port.lock, flags);
    spin_unlock_irqrestore(timer->base->lock, flags);

the above two cases hold lock with revert order, may
deadlock in SMP platform.

Signed-off-by: Zeng Zhaoming <b32542@freescale.com>

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index fd517262a8d07dbc401af568b2a75c352524a9c9..05147f43aaeff42190ceb5a8b25036cc0aa2c0b0 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -851,6 +851,8 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
        baud = uart_get_baud_rate(port, termios, old, 50, port->uartclk / 16);
        quot = uart_get_divisor(port, baud);
 
+       del_timer_sync(&sport->timer);
+
        spin_lock_irqsave(&sport->port.lock, flags);
 
        sport->port.read_status_mask = 0;
@@ -875,8 +877,6 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
                        sport->port.ignore_status_mask |= URXD_OVRRUN;
        }
 
-       del_timer_sync(&sport->timer);
-
        /*
         * Update the per-port timeout.
         */
@@ -940,10 +940,10 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
        /* set the parity, stop bits and data size */
        writel(ucr2 | old_txrxen, sport->port.membase + UCR2);
 
+       spin_unlock_irqrestore(&sport->port.lock, flags);
+
        if (UART_ENABLE_MS(&sport->port, termios->c_cflag))
                imx_enable_ms(&sport->port);
-
-       spin_unlock_irqrestore(&sport->port.lock, flags);
 }
 
 static const char *imx_type(struct uart_port *port)