[PATCH 3.11 192/198] USB: serial: fix potential runtime pm imbalance at device remove

[Luis Henriques]

3.11.10.13 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <jhovold at gmail.com>

commit c14829fad88dbeda57253590695b85ba51270621 upstream.

Only call usb_autopm_put_interface() if the corresponding
usb_autopm_get_interface() was successful.

This prevents a potential runtime PM counter imbalance should
usb_autopm_get_interface() fail. Note that the USB PM usage counter is
reset when the interface is unbound, but that the runtime PM counter may
be left unbalanced.

Also add comment on why we don't need to worry about racing
resume/suspend on autopm_get failures.

Fixes: d5fd650cfc7f ("usb: serial: prevent suspend/resume from racing
against probe/remove")

Signed-off-by: Johan Hovold <jhovold at gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/usb/serial/bus.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/serial/bus.c b/drivers/usb/serial/bus.c
index f053b302a00d..eef55b53c0b5 100644
--- a/drivers/usb/serial/bus.c
+++ b/drivers/usb/serial/bus.c
@@ -98,13 +98,19 @@ static int usb_serial_device_remove(struct device *dev)
 	struct usb_serial_port *port;
 	int retval = 0;
 	int minor;
+	int autopm_err;
 
 	port = to_usb_serial_port(dev);
 	if (!port)
 		return -ENODEV;
 
-	/* make sure suspend/resume doesn't race against port_remove */
-	usb_autopm_get_interface(port->serial->interface);
+	/*
+	 * Make sure suspend/resume doesn't race against port_remove.
+	 *
+	 * Note that no further runtime PM callbacks will be made if
+	 * autopm_get fails.
+	 */
+	autopm_err = usb_autopm_get_interface(port->serial->interface);
 
 	minor = port->minor;
 	tty_unregister_device(usb_serial_tty_driver, minor);
@@ -118,7 +124,9 @@ static int usb_serial_device_remove(struct device *dev)
 	dev_info(dev, "%s converter now disconnected from ttyUSB%d\n",
 		 driver->description, minor);
 
-	usb_autopm_put_interface(port->serial->interface);
+	if (!autopm_err)
+		usb_autopm_put_interface(port->serial->interface);
+
 	return retval;
 }
 
-- 
1.9.1