Re: [PATCH v9 16/17] vduse: Introduce VDUSE - vDPA Device in Userspace

On Wed, Jul 14, 2021 at 02:02:50PM +0800, Jason Wang wrote:

在 2021/7/14 下午1:54, Michael S. Tsirkin 写道:

quoted

On Wed, Jul 14, 2021 at 01:45:39PM +0800, Jason Wang wrote:

quoted

quoted

+static int vduse_dev_msg_sync(struct vduse_dev *dev,
+			      struct vduse_dev_msg *msg)
+{
+	int ret;
+
+	init_waitqueue_head(&msg->waitq);
+	spin_lock(&dev->msg_lock);
+	msg->req.request_id = dev->msg_unique++;
+	vduse_enqueue_msg(&dev->send_list, msg);
+	wake_up(&dev->waitq);
+	spin_unlock(&dev->msg_lock);
+
+	wait_event_killable_timeout(msg->waitq, msg->completed,
+				    VDUSE_REQUEST_TIMEOUT * HZ);
+	spin_lock(&dev->msg_lock);
+	if (!msg->completed) {
+		list_del(&msg->list);
+		msg->resp.result = VDUSE_REQ_RESULT_FAILED;
+	}
+	ret = (msg->resp.result == VDUSE_REQ_RESULT_OK) ? 0 : -EIO;

I think we should mark the device as malfunction when there is a timeout and
forbid any userspace operations except for the destroy aftwards for safety.

This looks like if one tried to run gdb on the program the behaviour
will change completely because kernel wants it to respond within
specific time. Looks like a receipe for heisenbugs.

Let's not build interfaces with arbitrary timeouts like that.
Interruptible wait exists for this very reason.

The problem is. Do we want userspace program like modprobe to be stuck for
indefinite time and expect the administrator to kill that?

Why would modprobe be stuck for forever?

Is this on the module probe path?