usb: gadget: f_ncm: remove spurious boolean timer_stopping

It is equivalent to ncm->netdev being NULL.

Cc: Brooke Basile <brookebasile@gmail.com>
Cc: "Bryan O'Donoghue" <bryan.odonoghue@linaro.org>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Link: https://lore.kernel.org/r/20210701114834.884597-2-zenczykowski@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_ncm.c

@@ -73,7 +73,6 @@ struct f_ncm {
 	struct sk_buff			*skb_tx_ndp;
 	u16				ndp_dgram_count;
 	struct hrtimer			task_timer;
-	bool				timer_stopping;
 };
 
 static inline struct f_ncm *func_to_ncm(struct usb_function *f)
@@ -889,7 +888,6 @@ static int ncm_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
 
 		if (ncm->port.in_ep->enabled) {
 			DBG(cdev, "reset ncm\n");
-			ncm->timer_stopping = true;
 			ncm->netdev = NULL;
 			gether_disconnect(&ncm->port);
 			ncm_reset_values(ncm);
@@ -927,7 +925,6 @@ static int ncm_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
 			if (IS_ERR(net))
 				return PTR_ERR(net);
 			ncm->netdev = net;
-			ncm->timer_stopping = false;
 		}
 
 		spin_lock(&ncm->lock);
@@ -1157,16 +1154,19 @@ static struct sk_buff *ncm_wrap_ntb(struct gether *port,
 static enum hrtimer_restart ncm_tx_timeout(struct hrtimer *data)
 {
 	struct f_ncm *ncm = container_of(data, struct f_ncm, task_timer);
+	struct net_device *netdev = READ_ONCE(ncm->netdev);
 
 	/* Only send if data is available. */
-	if (!ncm->timer_stopping && ncm->skb_tx_data) {
+	if (netdev && ncm->skb_tx_data) {
 		/* XXX This allowance of a NULL skb argument to ndo_start_xmit
 		 * XXX is not sane.  The gadget layer should be redesigned so
 		 * XXX that the dev->wrap() invocations to build SKBs is transparent
 		 * XXX and performed in some way outside of the ndo_start_xmit
 		 * XXX interface.
+		 *
+		 * This will call directly into u_ether's eth_start_xmit()
 		 */
-		ncm->netdev->netdev_ops->ndo_start_xmit(NULL, ncm->netdev);
+		netdev->netdev_ops->ndo_start_xmit(NULL, netdev);
 	}
 	return HRTIMER_NORESTART;
 }
@@ -1355,7 +1355,6 @@ static void ncm_disable(struct usb_function *f)
 	DBG(cdev, "ncm deactivated\n");
 
 	if (ncm->port.in_ep->enabled) {
-		ncm->timer_stopping = true;
 		ncm->netdev = NULL;
 		gether_disconnect(&ncm->port);
 	}