[ 17/20] usb: cdc-acm: fix devices not unthrottled on open

[Greg KH <gregkh@linuxfoundation.org>]

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

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

From: Otto Meta <otto.patches@sister-shadow.de>

commit 6c4707f3f8c44ec18282e1c014c80e1c257042f9 upstream.

Currently CDC-ACM devices stay throttled when their TTY is closed while
throttled, stalling further communication attempts after the next open.

Unthrottling during open/activate got lost starting with kernel
3.0.0 and this patch reintroduces it.

Signed-off-by: Otto Meta <otto.patches@sister-shadow.de>
Acked-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/class/cdc-acm.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -498,6 +498,14 @@ static int acm_tty_open(struct tty_struc
 
 	usb_autopm_put_interface(acm->control);
 
+	/*
+	 * Unthrottle device in case the TTY was closed while throttled.
+	 */
+	spin_lock_irq(&acm->read_lock);
+	acm->throttled = 0;
+	acm->throttle_req = 0;
+	spin_unlock_irq(&acm->read_lock);
+
 	if (acm_submit_read_urbs(acm, GFP_KERNEL))
 		goto bail_out;