usb: gadget: function: printer: avoid wrong list handling in printer_write()

When printer_write() calls usb_ep_queue(), a udc driver (e.g.
renesas_usbhs driver) may call usb_gadget_giveback_request() in
the udc .queue ops immediately. Then, printer_write() calls
list_add(&req->list, &dev->tx_reqs_active) wrongly. After that,
if we do unbind the printer driver, WARN_ON() happens in
printer_func_unbind() because the list entry is not removed.

So, this patch moves list_add(&req->list, &dev->tx_reqs_active)
calling before usb_ep_queue().

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_printer.c

@@ -631,19 +631,19 @@ printer_write(struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 			return -EAGAIN;
 		}
 
+		list_add(&req->list, &dev->tx_reqs_active);
+
 		/* here, we unlock, and only unlock, to avoid deadlock. */
 		spin_unlock(&dev->lock);
 		value = usb_ep_queue(dev->in_ep, req, GFP_ATOMIC);
 		spin_lock(&dev->lock);
 		if (value) {
+			list_del(&req->list);
 			list_add(&req->list, &dev->tx_reqs);
 			spin_unlock_irqrestore(&dev->lock, flags);
 			mutex_unlock(&dev->lock_printer_io);
 			return -EAGAIN;
 		}
-
-		list_add(&req->list, &dev->tx_reqs_active);
-
 	}
 
 	spin_unlock_irqrestore(&dev->lock, flags);