staging: unisys: visornic - ensure proper net locking in tx reset logic

visornic tx reset handling is done asynchronously via a workqueue in
visornic_timeout_reset().  As a result, it needs to use rtnl_lock() /
rtnl_unlock() to lock against possible simultaneous close() of the network
device.

(I consulted the bnx2 driver as a model here, as that driver also does
its tx reset handling asynchronously, just like visornic does.  See
bnx2_tx_timeout() and bnx2_reset_task().)
Signed-off-by: Tim Sell <Timothy.Sell@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/unisys/visornic/visornic_main.c

@@ -731,6 +731,12 @@ visornic_timeout_reset(struct work_struct *work)
 	devdata = container_of(work, struct visornic_devdata, timeout_reset);
 	netdev = devdata->netdev;
 
+	rtnl_lock();
+	if (!netif_running(netdev)) {
+		rtnl_unlock();
+		return;
+	}
+
 	response = visornic_disable_with_timeout(netdev,
 						 VISORNIC_INFINITE_RSP_WAIT);
 	if (response)
@@ -741,10 +747,13 @@ visornic_timeout_reset(struct work_struct *work)
 	if (response)
 		goto call_serverdown;
 
+	rtnl_unlock();
+
 	return;
 
 call_serverdown:
 	visornic_serverdown(devdata, NULL);
+	rtnl_unlock();
 }
 
 /**