drm: move lease init after validation in drm_lease_create

Patch bd36d3bab2e3d08f80766c86487090dbceed4651 fixed a deadlock in the
failure path of drm_lease_create. This made the partially initialized
lease object visible for a short window of time.

To avoid having the lessee state appear transiently, I've rearranged
the code so that the lessor fields are not filled in until the
parameters are all validated and the function will succeed.

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171221065424.1304-1-keithp@keithp.com

drivers/gpu/drm/drm_lease.c

@@ -220,17 +220,6 @@ static struct drm_master *drm_lease_create(struct drm_master *lessor, struct idr
 
 	mutex_lock(&dev->mode_config.idr_mutex);
 
-	/* Insert the new lessee into the tree */
-	id = idr_alloc(&(drm_lease_owner(lessor)->lessee_idr), lessee, 1, 0, GFP_KERNEL);
-	if (id < 0) {
-		error = id;
-		goto out_lessee;
-	}
-
-	lessee->lessee_id = id;
-	lessee->lessor = drm_master_get(lessor);
-	list_add_tail(&lessee->lessee_list, &lessor->lessees);
-
 	idr_for_each_entry(leases, entry, object) {
 		error = 0;
 		if (!idr_find(&dev->mode_config.crtc_idr, object))
@@ -246,6 +235,17 @@ static struct drm_master *drm_lease_create(struct drm_master *lessor, struct idr
 		}
 	}
 
+	/* Insert the new lessee into the tree */
+	id = idr_alloc(&(drm_lease_owner(lessor)->lessee_idr), lessee, 1, 0, GFP_KERNEL);
+	if (id < 0) {
+		error = id;
+		goto out_lessee;
+	}
+
+	lessee->lessee_id = id;
+	lessee->lessor = drm_master_get(lessor);
+	list_add_tail(&lessee->lessee_list, &lessor->lessees);
+
 	/* Move the leases over */
 	lessee->leases = *leases;
 	DRM_DEBUG_LEASE("new lessee %d %p, lessor %d %p\n", lessee->lessee_id, lessee, lessor->lessee_id, lessor);