Index: sys/vm/vm_object.c
===================================================================
--- sys/vm/vm_object.c
+++ sys/vm/vm_object.c
@@ -864,7 +864,6 @@
 		VM_OBJECT_WLOCK(backing_object);
 		if ((backing_object->flags & (OBJ_DEAD | OBJ_COLLAPSING)) == 0)
 			break;
-		VM_OBJECT_WUNLOCK(object);
 		vm_object_pip_sleep(backing_object, "vmbckwait");
 		counter_u64_add(object_collapse_waits, 1);
 		VM_OBJECT_WLOCK(object);