net: watchdog: hold device global xmit lock during tx disable

Prevent netif_tx_disable() running concurrently with dev_watchdog() by
taking the device global xmit lock. Otherwise, the recommended:

	netif_carrier_off(dev);
	netif_tx_disable(dev);

driver shutdown sequence can happen after the watchdog has already
checked carrier, resulting in possible false alarms. This is because
netif_tx_lock() only sets the frozen bit without maintaining the locks
on the individual queues.

Fixes: c3f26a26 ("netdev: Fix lockdep warnings in multiqueue configurations.")
Signed-off-by: Edwin Peer <edwin.peer@broadcom.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -4352,6 +4352,7 @@ static inline void netif_tx_disable(struct net_device *dev)
 
 	local_bh_disable();
 	cpu = smp_processor_id();
+	spin_lock(&dev->tx_global_lock);
 	for (i = 0; i < dev->num_tx_queues; i++) {
 		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
 
@@ -4359,6 +4360,7 @@ static inline void netif_tx_disable(struct net_device *dev)
 		netif_tx_stop_queue(txq);
 		__netif_tx_unlock(txq);
 	}
+	spin_unlock(&dev->tx_global_lock);
 	local_bh_enable();
 }