USB: cdc-acm: fix device unregistration

Unregister tty device in disconnect as is required by the USB stack.

By deferring unregistration to when the last tty reference is dropped,
the parent interface device can get unregistered before the child
resulting in broken hotplug events being generated when the tty is
finally closed:

KERNEL[2290.798128] remove   /devices/pci0000:00/0000:00:1d.7/usb2/2-1/2-1:3.1 (usb)
KERNEL[2290.804589] remove   /devices/pci0000:00/0000:00:1d.7/usb2/2-1 (usb)
KERNEL[2294.554799] remove   /2-1:3.1/tty/ttyACM0 (tty)

The driver must deal with tty callbacks after disconnect by checking the
disconnected flag. Specifically, further opens must be prevented and
this is already implemented.

Cc: stable <stable@vger.kernel.org>
Cc: Oliver Neukum <oneukum@suse.de>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index c125b61c24998cf69faea1372817de14240febcd..387dc6c8ad25b0d43a7d954ce71d877618fcb63d 100644 (file)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -593,7 +593,6 @@ static void acm_port_destruct(struct tty_port *port)
 
        dev_dbg(&acm->control->dev, "%s\n", __func__);
 
-       tty_unregister_device(acm_tty_driver, acm->minor);
        acm_release_minor(acm);
        usb_put_intf(acm->control);
        kfree(acm->country_codes);
@@ -1426,6 +1425,8 @@ static void acm_disconnect(struct usb_interface *intf)
 
        stop_data_traffic(acm);
 
+       tty_unregister_device(acm_tty_driver, acm->minor);
+
        usb_free_urb(acm->ctrlurb);
        for (i = 0; i < ACM_NW; i++)
                usb_free_urb(acm->wb[i].urb);