r8152: napi hangup fix after disconnect

When unplugging an r8152 adapter while the interface is UP, the NIC
becomes unusable.  usb->disconnect (aka rtl8152_disconnect) deletes
napi. Then, rtl8152_disconnect calls unregister_netdev and that invokes
netdev->ndo_stop (aka rtl8152_close). rtl8152_close tries to
napi_disable, but the napi is already deleted by disconnect above. So
the first while loop in napi_disable never finishes. This results in
complete deadlock of the network layer as there is rtnl_mutex held by
unregister_netdev.

So avoid the call to napi_disable in rtl8152_close when the device is
already gone.

The other calls to usb_kill_urb, cancel_delayed_work_sync,
netif_stop_queue etc. seem to be fine. The urb and netdev is not
destroyed yet.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: linux-usb@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/r8152.c

@@ -3962,7 +3962,8 @@ static int rtl8152_close(struct net_device *netdev)
 #ifdef CONFIG_PM_SLEEP
 	unregister_pm_notifier(&tp->pm_notifier);
 #endif
-	napi_disable(&tp->napi);
+	if (!test_bit(RTL8152_UNPLUG, &tp->flags))
+		napi_disable(&tp->napi);
 	clear_bit(WORK_ENABLE, &tp->flags);
 	usb_kill_urb(tp->intr_urb);
 	cancel_delayed_work_sync(&tp->schedule);