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authorAlex Williamson <alex.williamson@redhat.com>2017-06-19 09:10:32 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-07-27 15:06:07 -0700
commitdb42944cc63a2db5de17b6cb572327c7ab8ab637 (patch)
tree6ed34451eddc679289a8060d381ff9d1eb9e058a /drivers/vfio
parentfca8859982fb0e591c9baa10f1ba7c405dd5a120 (diff)
vfio: Fix group release deadlock
commit 811642d8d8a82c0cce8dc2debfdaf23c5a144839 upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 6070b793cbcb..402d54f963e4 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -296,6 +296,34 @@ 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)
{
@@ -620,7 +648,14 @@ 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;
}