+ /* If blocked by the write barrier, then return "-EINPROGRESS"
+ * to the caller. Usually, such error will be forwarded to the
+ * client, and the expected behaviour is to re-try such modify
+ * RPC some time later until the barrier is thawed or expired. */
+ if (unlikely(!barrier_entry(mdd->mdd_bottom)))
+ return ERR_PTR(-EINPROGRESS);
+