[PATCH 24/75] tty: Fix close races in USB serial

Alan Cox
2009-01-02T13:43:49Z

From: Alan Cox <alan@redhat.com>

USB serial has always had races where the tty port usage count can hit zero
during a receive event. The internal locking is a mutex so we can't use
that in the IRQ handlers.

With krefs we can tackle this differently but we still need to be careful.

Signed-off-by: Alan Cox <alan@redhat.com>
---

drivers/usb/serial/usb-serial.c | 15 ++++++++++-----
1 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 794b5ff..aafa684 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -269,15 +269,19 @@ static void serial_close(struct tty_struct *tty, struct file *filp)
return;
}

- --port->port.count;
- if (port->port.count == 0)
+ if (port->port.count == 1)
/* only call the device specific close if this
- * port is being closed by the last owner */
+ * port is being closed by the last owner. Ensure we do
+ * this before we drop the port count. The call is protected
+ * by the port mutex
+ */
port->serial->type->close(tty, port, filp);

- if (port->port.count == (port->console? 1 : 0)) {
+ if (port->port.count == (port->console ? 2 : 1)) {
struct tty_struct *tty = tty_port_tty_get(&port->port);
if (tty) {
+ /* We must do this before we drop the port count to
+ zero. */
if (tty->driver_data)
tty->driver_data = NULL;
tty_port_tty_set(&port->port, NULL);
@@ -285,13 +289,14 @@ static void serial_close(struct tty_struct *tty, struct file *filp)
}
}

- if (port->port.count == 0) {
+ if (port->port.count == 1) {
mutex_lock(&port->serial->disc_mutex);
if (!port->serial->disconnected)
usb_autopm_put_interface(port->serial->interface);
mutex_unlock(&port->serial->disc_mutex);
module_put(port->serial->type->driver.owner);
}
+ --port->port.count;

mutex_unlock(&port->mutex);
usb_serial_put(port->serial);