staging: usbip: vhci: fix oops on subsequent attach

vhci_rx/vhci_tx threads are created once but stopped each
time the vdev is shut down. On subsequent attach wake_up_process()
oopses trying to access the stopped threads.

This patch does as before the kthread conversion which is to
create the threads each time a device is attached and stop the
threads when the device is shut down.
Signed-off-by: Max Vozeler <max@hinterhof.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Takahiro Hirofuchi <hirofuchi@users.sourceforge.net>
Cc: Arjan Mels <arjan.mels@gmx.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/usbip/vhci_hcd.c

@@ -876,8 +876,10 @@ static void vhci_shutdown_connection(struct usbip_device *ud)
 	}
 
 	/* kill threads related to this sdev, if v.c. exists */
-	kthread_stop(vdev->ud.tcp_rx);
-	kthread_stop(vdev->ud.tcp_tx);
+	if (vdev->ud.tcp_rx)
+		kthread_stop(vdev->ud.tcp_rx);
+	if (vdev->ud.tcp_tx)
+		kthread_stop(vdev->ud.tcp_tx);
 
 	usbip_uinfo("stop threads\n");
 
@@ -949,9 +951,6 @@ static void vhci_device_init(struct vhci_device *vdev)
 {
 	memset(vdev, 0, sizeof(*vdev));
 
-	vdev->ud.tcp_rx = kthread_create(vhci_rx_loop, &vdev->ud, "vhci_rx");
-	vdev->ud.tcp_tx = kthread_create(vhci_tx_loop, &vdev->ud, "vhci_tx");
-
 	vdev->ud.side   = USBIP_VHCI;
 	vdev->ud.status = VDEV_ST_NULL;
 	/* vdev->ud.lock   = SPIN_LOCK_UNLOCKED; */

drivers/staging/usbip/vhci_sysfs.c

@@ -21,6 +21,7 @@
 #include "vhci.h"
 
 #include <linux/in.h>
+#include <linux/kthread.h>
 
 /* TODO: refine locking ?*/
 
@@ -220,13 +221,13 @@ static ssize_t store_attach(struct device *dev, struct device_attribute *attr,
 	vdev->ud.tcp_socket = socket;
 	vdev->ud.status     = VDEV_ST_NOTASSIGNED;
 
-	wake_up_process(vdev->ud.tcp_rx);
-	wake_up_process(vdev->ud.tcp_tx);
-
 	spin_unlock(&vdev->ud.lock);
 	spin_unlock(&the_controller->lock);
 	/* end the lock */
 
+	vdev->ud.tcp_rx = kthread_run(vhci_rx_loop, &vdev->ud, "vhci_rx");
+	vdev->ud.tcp_tx = kthread_run(vhci_tx_loop, &vdev->ud, "vhci_tx");
+
 	rh_port_connect(rhport, speed);
 
 	return count;