I cloned git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux.git as you are testing changes there.
> commit 09e4522c87ff54c655c09f318a68b012eda8eb01 (HEAD -> usbip_test, origin/usbip_test)
> Author: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
> Date: Thu Mar 11 11:18:25 2021 -0700
>
> usbip: fix vhci races in connection tear down
>
> - Change vhci_device_reset() to reset tcp_socket and sockfd.
> if !in_disconnect
How it can happen? vhci_device_reset() can be called only after vhci_shutdown_connection()
completed, and vhci_shutdown_connection() from subsequent requests cannot be called until
vhci_device_reset() completes. I consider it as a dead code which should be removed by
my "[PATCH v4 05/12] usb: usbip: don't reset tcp_socket at vhci_device_reset()".
And what you are missing in your [PATCH 4,5,6/6] is
diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
index c4457026d5ad..3c64bd06ab53 100644
--- a/drivers/usb/usbip/vhci_sysfs.c
+++ b/drivers/usb/usbip/vhci_sysfs.c
@@ -423,6 +423,7 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
/* end the lock */
wake_up_process(vdev->ud.tcp_rx);
+ schedule_timeout_uninterruptible(HZ); // Consider being preempted here.
wake_up_process(vdev->ud.tcp_tx);
rh_port_connect(vdev, speed);
. wake_up_process(tcp_tx) can call vhci_shutdown_connection() before wake_up_process(tcp_tx) is called.
Since vhci_shutdown_connection() destroys tcp_tx thread and releases tcp_tx memory via kthread_stop_put(tcp_tx),
wake_up_process(tcp_tx) will access already freed memory. Your patch converted "NULL pointer dereference caused by
failing to call kthread_stop_put(tcp_tx)" into "use after free caused by succeeding to call kthread_stop_put(tcp_tx)".
