ath9k_htc: fix data race between request_firmware_nowait() callback and suspend()

ath9k_hif_usb_probe() requests firmware asynchronically and
there is some initialization postponed till firmware is ready.
In particular, ath9k_hif_usb_firmware_cb() callback initializes
hif_dev->tx.tx_buf and hif_dev->tx.tx_pending lists.

At the same time, ath9k_hif_usb_suspend() iterates that lists through
ath9k_hif_usb_dealloc_urbs(). If suspend happens before request_firmware_nowait()
callback is called, it can lead to oops.

Similar issue could be in ath9k_hif_usb_disconnect(), but it is prevented
using hif_dev->fw_done completion and HIF_USB_READY flag. The patch extends
this approach to suspend() as well.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/hif_usb.c

@@ -1082,7 +1082,7 @@ static void ath9k_hif_usb_firmware_fail(struct hif_device_usb *hif_dev)
 	struct device *dev = &hif_dev->udev->dev;
 	struct device *parent = dev->parent;
 
-	complete(&hif_dev->fw_done);
+	complete_all(&hif_dev->fw_done);
 
 	if (parent)
 		device_lock(parent);
@@ -1131,7 +1131,7 @@ static void ath9k_hif_usb_firmware_cb(const struct firmware *fw, void *context)
 
 	release_firmware(fw);
 	hif_dev->flags |= HIF_USB_READY;
-	complete(&hif_dev->fw_done);
+	complete_all(&hif_dev->fw_done);
 
 	return;
 
@@ -1316,6 +1316,9 @@ static int ath9k_hif_usb_suspend(struct usb_interface *interface,
 	if (!(hif_dev->flags & HIF_USB_START))
 		ath9k_htc_suspend(hif_dev->htc_handle);
 
+	wait_for_completion(&hif_dev->fw_done);
+
+	if (hif_dev->flags & HIF_USB_READY)
 		ath9k_hif_usb_dealloc_urbs(hif_dev);
 
 	return 0;