[PATCH] serial: fix possible imx deadlock

[John Ogness]

This patch fixes a possible deadlock situation with the port and timer
locks. The calling paths for the deadlock situation are:

1. imx_set_termios() -> LOCK(port.lock)
      -> del_timer_sync() -> LOCK(timer.base.lock)

2. run_timer_softirq() -> LOCK(timer.base.lock)
      -> imx_timeout() -> LOCK(port.lock)

This patch is against 2.6.34-rc1.

Signed-off-by: John Ogness <john.ogness at linutronix.de>
---
 drivers/serial/imx.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
diff -Naurp a/drivers/serial/imx.c b/drivers/serial/imx.c
--- a/drivers/serial/imx.c	2010-03-08 19:45:44.000000000 +0100
+++ b/drivers/serial/imx.c	2010-03-15 09:52:39.855261060 +0100
@@ -836,6 +836,12 @@ imx_set_termios(struct uart_port *port, 
 	baud = uart_get_baud_rate(port, termios, old, 50, port->uartclk / 16);
 	quot = uart_get_divisor(port, baud);
 
+	/*
+	 * Stop our timer. This is done with the port unlocked
+	 * to avoid possible deadlock against the timer function.
+	 */
+	del_timer_sync(&sport->timer);
+
 	spin_lock_irqsave(&sport->port.lock, flags);
 
 	sport->port.read_status_mask = 0;
@@ -860,8 +866,6 @@ imx_set_termios(struct uart_port *port, 
 			sport->port.ignore_status_mask |= URXD_OVRRUN;
 	}
 
-	del_timer_sync(&sport->timer);
-
 	/*
 	 * Update the per-port timeout.
 	 */