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authorAlex Williamson <alex.williamson@redhat.com>2017-06-19 09:10:32 -0600
committerAlex Williamson <alex.williamson@redhat.com>2017-06-28 13:49:38 -0600
commit811642d8d8a82c0cce8dc2debfdaf23c5a144839 (patch)
tree8b64ef6d040f88ec61d6c12c82ebdb43843c3712 /drivers/vfio
parent7b3a10df1d4bd8a83934897442370221b4cd631b (diff)
downloadlinux-811642d8d8a82c0cce8dc2debfdaf23c5a144839.tar.bz2
vfio: Fix group release deadlock
If vfio_iommu_group_notifier() acquires a group reference and that reference becomes the last reference to the group, then vfio_group_put introduces a deadlock code path where we're trying to unregister from the iommu notifier chain from within a callout of that chain. Use a work_struct to release this reference asynchronously. Signed-off-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Eric Auger <eric.auger@redhat.com> Tested-by: Eric Auger <eric.auger@redhat.com> Cc: stable@vger.kernel.org
Diffstat (limited to 'drivers/vfio')
-rw-r--r--drivers/vfio/vfio.c37
1 files changed, 36 insertions, 1 deletions
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 6a49485eb49d..54dd2fbf83d9 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -423,6 +423,34 @@ static void vfio_group_put(struct vfio_group *group)
kref_put_mutex(&group->kref, vfio_group_release, &vfio.group_lock);
}
+struct vfio_group_put_work {
+ struct work_struct work;
+ struct vfio_group *group;
+};
+
+static void vfio_group_put_bg(struct work_struct *work)
+{
+ struct vfio_group_put_work *do_work;
+
+ do_work = container_of(work, struct vfio_group_put_work, work);
+
+ vfio_group_put(do_work->group);
+ kfree(do_work);
+}
+
+static void vfio_group_schedule_put(struct vfio_group *group)
+{
+ struct vfio_group_put_work *do_work;
+
+ do_work = kmalloc(sizeof(*do_work), GFP_KERNEL);
+ if (WARN_ON(!do_work))
+ return;
+
+ INIT_WORK(&do_work->work, vfio_group_put_bg);
+ do_work->group = group;
+ schedule_work(&do_work->work);
+}
+
/* Assume group_lock or group reference is held */
static void vfio_group_get(struct vfio_group *group)
{
@@ -762,7 +790,14 @@ static int vfio_iommu_group_notifier(struct notifier_block *nb,
break;
}
- vfio_group_put(group);
+ /*
+ * If we're the last reference to the group, the group will be
+ * released, which includes unregistering the iommu group notifier.
+ * We hold a read-lock on that notifier list, unregistering needs
+ * a write-lock... deadlock. Release our reference asynchronously
+ * to avoid that situation.
+ */
+ vfio_group_schedule_put(group);
return NOTIFY_OK;
}