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Subject[006/102] Staging: usbip: vhci-hcd: Do not kill already dead RX/TX kthread
3.0-stable review patch.  If anyone has any objections, please let us know.


From: Tobias Klauser <>

commit 8547d4cc2b616e4f1dafebe2c673fc986422b506 upstream.

When unbinding a device on the host which was still attached on the
client, I got a NULL pointer dereference on the client. This turned out
to be due to kthread_stop() being called on an already dead kthread.

Here is how I was able to reproduce the problem:

server:# usbip bind -b 1-2
client:# usbip attach -h server -b 1-2
server:# usbip unbind -b 1-2

This patch fixes the problem by checking the kthread before attempting
to kill it, as it is done on the opposite side in

Signed-off-by: Tobias Klauser <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/staging/usbip/vhci_hcd.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/staging/usbip/vhci_hcd.c
+++ b/drivers/staging/usbip/vhci_hcd.c
@@ -846,9 +846,9 @@ static void vhci_shutdown_connection(str

/* kill threads related to this sdev, if v.c. exists */
- if (vdev->ud.tcp_rx)
+ if (vdev->ud.tcp_rx && !task_is_dead(vdev->ud.tcp_rx))
- if (vdev->ud.tcp_tx)
+ if (vdev->ud.tcp_tx && !task_is_dead(vdev->ud.tcp_tx))

pr_info("stop threads\n");

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