staging: usbip: fix the usage of kthread_stop()

stub_shutdown_connection() and vhci_shutdown_connection() use
task_is_dead() before kthread_stop(). This buys nothing and wrong.
kthread_stop() is fine even if this thread is dead. However, if it
is dead nothing protects this task_struct, we shouldn't touch this
memory.

Change the code to do the necessary get_task_struct/put_task_struct.

This patch assumes that

	- xxx_shutdown_connection() is always called, so we can't
	  leak the task_struct.

	- kthread_stop_put() can't be called twice on the same task.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Tobias Klauser <tklauser@distanz.ch>
Cc: Matt Mooney <mfm@muteddisk.com>,
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/staging/usbip/vhci_hcd.c b/drivers/staging/usbip/vhci_hcd.c
index dca9bf11f0c2..f708cbaee16b 100644
--- a/drivers/staging/usbip/vhci_hcd.c
+++ b/drivers/staging/usbip/vhci_hcd.c
@@ -821,10 +821,10 @@ static void vhci_shutdown_connection(struct usbip_device *ud)
 	}
 
 	/* kill threads related to this sdev, if v.c. exists */
-	if (vdev->ud.tcp_rx && !task_is_dead(vdev->ud.tcp_rx))
-		kthread_stop(vdev->ud.tcp_rx);
-	if (vdev->ud.tcp_tx && !task_is_dead(vdev->ud.tcp_tx))
-		kthread_stop(vdev->ud.tcp_tx);
+	if (vdev->ud.tcp_rx)
+		kthread_stop_put(vdev->ud.tcp_rx);
+	if (vdev->ud.tcp_tx)
+		kthread_stop_put(vdev->ud.tcp_tx);
 
 	pr_info("stop threads\n");