On 2021/03/08 16:35, Tetsuo Handa wrote:

On 2021/03/08 12:53, Shuah Khan wrote:

quoted

Fix the above problems:
- Stop using kthread_get_run() macro to create/start threads.
- Create threads and get task struct reference.
- Add kthread_create() failure handling and bail out.
- Hold usbip_device lock to update local and shared states after
  creating rx and tx threads.
- Update usbip_device status to SDEV_ST_USED.
- Update usbip_device tcp_socket, sockfd, tcp_rx, and tcp_tx
- Start threads after usbip_device (tcp_socket, sockfd, tcp_rx, tcp_tx,
  and status) is complete.

No, the whole usbip_sockfd_store() etc. should be serialized using a mutex,
for two different threads can open same file and write the same content at
the same moment. This results in seeing SDEV_ST_AVAILABLE and creating two
threads and overwiting global variables and setting SDEV_ST_USED and starting
two threads by each of two thread, which will later fail to call kthread_stop()
on one of two thread because global variables are overwritten.

kthread_crate() (which involves GFP_KERNEL allocation) can take long time
enough to hit

  usbip_sockfd_store() must perform

      if (sdev->ud.status != SDEV_ST_AVAILABLE) {

Oops. This is

	if (sdev->ud.status == SDEV_ST_AVAILABLE) {

of course.

        /* misc assignments for attach operation */
        sdev->ud.status = SDEV_ST_USED;
      }

  under a lock, or multiple ud->tcp_{tx,rx} are created (which will later
  cause a crash like [1]) and refcount on ud->tcp_socket is leaked when
  usbip_sockfd_store() is concurrently called.

problem. That's why my patch introduced usbip_event_mutex lock.

And I think that same serialization is required between "rh_port_connect() from attach_store()" and
"rh_port_disconnect() from vhci_shutdown_connection() via usbip_event_add(&vdev->ud, VDEV_EVENT_DOWN)
 from vhci_port_disconnect() from detach_store()", for both vhci_rx_pdu() from vhci_rx_loop() and
vhci_port_disconnect() from detach_store() can queue VDEV_EVENT_DOWN event which can be processed
without waiting for attach_store() to complete.