net: pxa168_eth: Fix a potential data race in pxa168_eth_remove

pxa168_eth_remove() firstly calls unregister_netdev(),
then cancels a timeout work. unregister_netdev() shuts down a device
interface and removes it from the kernel tables. If the timeout occurs
in parallel, the timeout work (pxa168_eth_tx_timeout_task) performs stop
and open of the device. It may lead to an inconsistent state and memory
leaks.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: NPavel Andrianov <andrianov@ispras.ru>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/pxa168_eth.c

@@ -1544,8 +1544,8 @@ static int pxa168_eth_remove(struct platform_device *pdev)
 	clk_disable_unprepare(pep->clk);
 	mdiobus_unregister(pep->smi_bus);
 	mdiobus_free(pep->smi_bus);
-	unregister_netdev(dev);
 	cancel_work_sync(&pep->tx_timeout_task);
+	unregister_netdev(dev);
 	free_netdev(dev);
 	return 0;
 }