staging: usbip: fix shutdown problems.

When shuting down the tcp_rx and tcp_tx threads first check if they are
not closed already (maybe because an error caused them to return).

Signed-off-by: Arjan Mels <arjan.mels@gmx.net>
Cc: Takahiro Hirofuchi <hirofuchi@users.sourceforge.net>
Cc: Max Vozeler <max@vozeler.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/usbip/stub_dev.c

@@ -220,8 +220,10 @@ static void stub_shutdown_connection(struct usbip_device *ud)
 	}
 
 	/* 1. stop threads */
-	kthread_stop(ud->tcp_rx);
-	kthread_stop(ud->tcp_tx);
+	if (ud->tcp_rx && !task_is_dead(ud->tcp_rx))
+		kthread_stop(ud->tcp_rx);
+	if (ud->tcp_tx && !task_is_dead(ud->tcp_tx))
+		kthread_stop(ud->tcp_tx);
 
 	/* 2. close the socket */
 	/*