tty: serial: imx: console write routing is unsafe on SMP

commit 9ec1882df244c4ee1baa692676fef5e8b0f5487d upstream.

The console feature's write routing is unsafe on SMP with
the startup/shutdown call.

There could be several consumers of the console
* the kernel printk
* the init process using /dev/kmsg to call printk to show log
* shell, which open /dev/console and write with sys_write()

The shell goes into the normal uart open/write routing,
but the other two go into the console operations.
The open routing calls imx serial startup, which will write USR1/2
register without any lock and critical with imx_console_write call.

Add a spin_lock for startup/shutdown/console_write routing.

This patch is a port from Freescale's Android kernel.

Signed-off-by: Xinyu Chen <xinyu.chen@freescale.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
CC: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 163fc9021f5ad58a695c0fded23a300ed49b4627..2351ebe855aae6e3a72b51dbca1e7a4988fcc538 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -725,6 +725,7 @@ static int imx_startup(struct uart_port *port)
                }
        }
 
+       spin_lock_irqsave(&sport->port.lock, flags);
        /*
         * Finally, clear and enable interrupts
         */
@@ -778,7 +779,6 @@ static int imx_startup(struct uart_port *port)
        /*
         * Enable modem status interrupts
         */
-       spin_lock_irqsave(&sport->port.lock,flags);
        imx_enable_ms(&sport->port);
        spin_unlock_irqrestore(&sport->port.lock,flags);
 
@@ -808,10 +808,13 @@ static void imx_shutdown(struct uart_port *port)
 {
        struct imx_port *sport = (struct imx_port *)port;
        unsigned long temp;
+       unsigned long flags;
 
+       spin_lock_irqsave(&sport->port.lock, flags);
        temp = readl(sport->port.membase + UCR2);
        temp &= ~(UCR2_TXEN);
        writel(temp, sport->port.membase + UCR2);
+       spin_unlock_irqrestore(&sport->port.lock, flags);
 
        if (USE_IRDA(sport)) {
                struct imxuart_platform_data *pdata;
@@ -840,12 +843,14 @@ static void imx_shutdown(struct uart_port *port)
         * Disable all interrupts, port and break condition.
         */
 
+       spin_lock_irqsave(&sport->port.lock, flags);
        temp = readl(sport->port.membase + UCR1);
        temp &= ~(UCR1_TXMPTYEN | UCR1_RRDYEN | UCR1_RTSDEN | UCR1_UARTEN);
        if (USE_IRDA(sport))
                temp &= ~(UCR1_IREN);
 
        writel(temp, sport->port.membase + UCR1);
+       spin_unlock_irqrestore(&sport->port.lock, flags);
 }
 
 static void
@@ -1119,6 +1124,9 @@ imx_console_write(struct console *co, const char *s, unsigned int count)
 {
        struct imx_port *sport = imx_ports[co->index];
        unsigned int old_ucr1, old_ucr2, ucr1;
+       unsigned long flags;
+
+       spin_lock_irqsave(&sport->port.lock, flags);
 
        /*
         *      First, save UCR1/2 and then disable interrupts
@@ -1145,6 +1153,8 @@ imx_console_write(struct console *co, const char *s, unsigned int count)
 
        writel(old_ucr1, sport->port.membase + UCR1);
        writel(old_ucr2, sport->port.membase + UCR2);
+
+       spin_unlock_irqrestore(&sport->port.lock, flags);
 }
 
 /*