-When accessing a key's payload data, the key->lock should be at least read
-locked, or else the data may be changed by update during the access.
+When accessing a key's payload data, key->lock should be at least read locked,
+or else the data may be changed by an update being performed from userspace
+whilst the driver or filesystem is trying to access it. If no update method is
+supplied, then the key's payload may be accessed without holding a lock as
+there is no way to change it, provided it can be guaranteed that the key's
+type definition won't go away.