Re: [PATCH v13 09/15] s390/vfio-ap: allow hot plug/unplug of AP resources using mdev device

On Wed, 3 Feb 2021 18:13:09 -0500
Tony Krowiak [off-list ref] wrote:

On 1/12/21 12:55 PM, Halil Pasic wrote:

quoted

On Tue, 12 Jan 2021 02:12:51 +0100
Halil Pasic [off-list ref] wrote:
 

quoted

quoted

@@ -1347,8 +1437,11 @@ void vfio_ap_mdev_remove_queue(struct ap_device *apdev)
  	apqi = AP_QID_QUEUE(q->apqn);
  	vfio_ap_mdev_reset_queue(apid, apqi, 1);
  
-	if (q->matrix_mdev)
+	if (q->matrix_mdev) {
+		matrix_mdev = q->matrix_mdev;
  		vfio_ap_mdev_unlink_queue(q);
+		vfio_ap_mdev_refresh_apcb(matrix_mdev);
+	}
  
  	kfree(q);
  	mutex_unlock(&matrix_dev->lock);  

Shouldn't we first remove the queue from the APCB and then
reset? Sorry, I missed this one yesterday.  

I agreed to move the reset, however if the remove callback is
invoked due to a manual unbind of the queue and the queue is
in use by a guest, the cleanup of the IRQ resources after the
reset of the queue will not happen because the link from the
queue to the matrix mdev was removed. Consequently, I'm going
to have to change the patch 05/15 to split the vfio_ap_mdev_unlink_queue()
function into two functions: one to remove the link from the matrix mdev to
the queue; and, one to remove the link from the queue to the matrix
mdev. 

Does that mean we should reset before the unlink (or before the second
part of it after the split up)?

I mean have a look at unassign_adapter_store() with all patches
of this series applied. It does an unlink but doesn't do any reset,
or cleanup IRQ resources. And after the unlink we can't clean up
the IRQ resources properly.

But before all this we should resolve this circular lock dependency
problem in a satisfactory way. I'm quite worried about how it is going
to mesh with this series and dynamic ap pass-through.

Regards,
Halil

Only the first will be used for the remove callback which should
be fine since the queue object is freed at the end of the remove
function anyway.

quoted

Regards,
Halil