Patch "vfio: Rework group release notifier warning" has been added to the 4.10-stable tree

This is a note to let you know that I've just added the patch titled

vfio: Rework group release notifier warning

to the 4.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
vfio-rework-group-release-notifier-warning.patch
and it can be found in the queue-4.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alex Williamson <[email protected]>
Date: Tue, 21 Mar 2017 13:19:09 -0600
Subject: vfio: Rework group release notifier warning

From: Alex Williamson <[email protected]>

commit 65b1adebfe43c642dfe3b109edb5d992db5fbe72 upstream.

The intent of the original warning is make sure that the mdev vendor driver has removed any group notifiers at the point where the group is closed by the user. Theoretically this would be through an orderly shutdown where any devices are release prior to the group release. We can't always count on an orderly shutdown, the user can close the group before the notifier can be removed or the user task might be killed. We'd like to add this sanity test when the group is idle and the only references are from the devices within the group themselves, but we don't have a good way to do that. Instead check both when the group itself is removed and when the group is opened. A bit later than we'd prefer, but better than the current over aggressive approach.

---
 drivers/vfio/vfio.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

@@ -403,6 +403,7 @@ static void vfio_group_release(struct kr
 	struct iommu_group *iommu_group = group->iommu_group;
 
 	WARN_ON(!list_empty(&group->device_list));
+	WARN_ON(group->notifier.head);
 
 	list_for_each_entry_safe(unbound, tmp,
 				 &group->unbound_list, unbound_next) {

@@ -1573,6 +1574,10 @@ static int vfio_group_fops_open(struct i
 		return -EBUSY;
 	}
 
+	/* Warn if previous user didn't cleanup and re-init to drop them */
+	if (WARN_ON(group->notifier.head))
+		BLOCKING_INIT_NOTIFIER_HEAD(&group->notifier);
+
 	filep->private_data = group;
 
 	return 0;

@@ -1584,9 +1589,6 @@ static int vfio_group_fops_release(struc
 
 	filep->private_data = NULL;
 
-	/* Any user didn't unregister? */
-	WARN_ON(group->notifier.head);
-
 	vfio_group_try_dissolve_container(group);
 
 	atomic_dec(&group->opened);

Patches currently in stable-queue which might be from [email protected] are

queue-4.10/vfio-rework-group-release-notifier-warning.patch