[PATCH 3.12 058/133] tty/serial: at91: disable uart timer at start of shutdown

Greg Kroah-Hartman
2014-02-04T22:16:59Z

From: Marek Roszko <mark.roszko@gmail.com>

commit 8bc661bfc0c2d221e209f4205bdaaf574d50100c upstream.

The uart timer will schedule a tasklet when it fires. It is possible that it
can fire inside _shutdown before it is killed in the dma and pdc cleanup
routines. This causes a tasklet that exists after the port is shutdown, so when
the kernel finally executes it, it panics as the tty port is NULL.

This is a somewhat rare condition but its possible if a program keeps on
opening/closing the port. It has been observed in particular with systemd
boot messages that were causing a kernel panic because of this behavior.

Moving the timer deletion to the beginning of the function stops a tasklet from
being scheduled unexpectedly.

Signed-off-by: Marek Roszko <mark.roszko@gmail.com>
[nicolas.ferre@atmel.com: modify commit message, call setup_timer() in any case]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/tty/serial/atmel_serial.c | 22 ++++++++++------------
1 file changed, 10 insertions(+), 12 deletions(-)

--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -824,9 +824,6 @@ static void atmel_release_rx_dma(struct
atmel_port->desc_rx = NULL;
atmel_port->chan_rx = NULL;
atmel_port->cookie_rx = -EINVAL;
-
- if (!atmel_port->is_usart)
- del_timer_sync(&atmel_port->uart_timer);
}

static void atmel_rx_from_dma(struct uart_port *port)
@@ -1228,9 +1225,6 @@ static void atmel_release_rx_pdc(struct
DMA_FROM_DEVICE);
kfree(pdc->buf);
}
-
- if (!atmel_port->is_usart)
- del_timer_sync(&atmel_port->uart_timer);
}

static void atmel_rx_from_pdc(struct uart_port *port)
@@ -1587,12 +1581,13 @@ static int atmel_startup(struct uart_por
/* enable xmit & rcvr */
UART_PUT_CR(port, ATMEL_US_TXEN | ATMEL_US_RXEN);

+ setup_timer(&atmel_port->uart_timer,
+ atmel_uart_timer_callback,
+ (unsigned long)port);
+
if (atmel_use_pdc_rx(port)) {
/* set UART timeout */
if (!atmel_port->is_usart) {
- setup_timer(&atmel_port->uart_timer,
- atmel_uart_timer_callback,
- (unsigned long)port);
mod_timer(&atmel_port->uart_timer,
jiffies + uart_poll_timeout(port));
/* set USART timeout */
@@ -1607,9 +1602,6 @@ static int atmel_startup(struct uart_por
} else if (atmel_use_dma_rx(port)) {
/* set UART timeout */
if (!atmel_port->is_usart) {
- setup_timer(&atmel_port->uart_timer,
- atmel_uart_timer_callback,
- (unsigned long)port);
mod_timer(&atmel_port->uart_timer,
jiffies + uart_poll_timeout(port));
/* set USART timeout */
@@ -1635,6 +1627,12 @@ static void atmel_shutdown(struct uart_p
struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

/*
+ * Prevent any tasklets being scheduled during
+ * cleanup
+ */
+ del_timer_sync(&atmel_port->uart_timer);
+
+ /*
* Clear out any scheduled tasklets before
* we destroy the buffers
*/