usb: cdc-acm: handle unlinked urb in acm read callback

In current acm driver, the bulk-in callback function ignores the
URBs unlinked in usb core.

This causes unexpected data loss in some cases. For example,
runtime suspend entry will unlinked all urbs and set urb->status
to -ENOENT even those urbs might have data not processed yet.
Hence, data loss occurs.

This patch lets bulk-in callback function handle unlinked urbs
to avoid data loss.
Signed-off-by: Tang Jian Qiang <jianqiang.tang@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Cc: stable@vger.kernel.org
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.c

@@ -428,7 +428,8 @@ static void acm_read_bulk_callback(struct urb *urb)
 		set_bit(rb->index, &acm->read_urbs_free);
 		dev_dbg(&acm->data->dev, "%s - non-zero urb status: %d\n",
 							__func__, status);
-		return;
+		if ((status != -ENOENT) || (urb->actual_length == 0))
+			return;
 	}
 
 	usb_mark_last_busy(acm->dev);