On 2021/03/08 12:53, Shuah Khan wrote:
> 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) {
/* 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.
