staging: usbip: Fix deadlock

When detaching a port from the client side (usbip --detach 0),
the event thread, on the server side, is going to deadlock.
The "eh" server thread is getting USBIP_EH_RESET event and calls:
-> stub_device_reset() -> usb_reset_device()
the USB framework is then calling back _in the same "eh" thread_ :
-> stub_disconnect() -> usbip_stop_eh() -> wait_for_completion()
the "eh" thread is being asleep forever, waiting for its own completion.
This patch checks if "eh" is the current thread, in usbip_stop_eh().

Signed-off-by: Eric Lescouet <[e-mail]>
Cc: stable <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/usbip/usbip_event.c

···
 {
 	struct usbip_task *eh = &ud->eh;
 
+	if (eh->thread == current)
+		return; /* do not wait for myself */
+
 	wait_for_completion(&eh->thread_done);
 	usbip_dbg_eh("usbip_eh has finished\n");
 }