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Subject[ 110/135] tty: serial: imx: console write routing is unsafe on SMP
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Xinyu Chen <xinyu.chen@freescale.com>

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>
---
drivers/tty/serial/imx.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -725,6 +725,7 @@ static int imx_startup(struct uart_port
}
}

+ spin_lock_irqsave(&sport->port.lock, flags);
/*
* Finally, clear and enable interrupts
*/
@@ -778,7 +779,6 @@ static int imx_startup(struct uart_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_por
{
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_por
* 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, co
{
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, co

writel(old_ucr1, sport->port.membase + UCR1);
writel(old_ucr2, sport->port.membase + UCR2);
+
+ spin_unlock_irqrestore(&sport->port.lock, flags);
}

/*



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