nfsd: only check RPC_SIGNALLED() when restarting rpc_task

nfsd4_cb_sequence_done() currently checks RPC_SIGNALLED() when
processing the compound and releasing the slot. If RPC_SIGNALLED()
returns true, then that means that the client is going to be torn down.

Don't check RPC_SIGNALLED() after processing a successful reply. Check
it only before restarting the rpc_task. If it returns true, then requeue
the callback instead of restarting the task.

Also, handle rpc_restart_call() and rpc_restart_call_prepare() failures
correctly, by requeueing the callback.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: jtlayton

fs/nfsd/nfs4callback.c

@@ -1379,8 +1379,8 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
 		goto requeue;
 	case -NFS4ERR_DELAY:
 		cb->cb_seq_status = 1;
-		if (!rpc_restart_call(task))
-			goto out;
+		if (RPC_SIGNALLED(task) || !rpc_restart_call(task))
+			goto requeue;
 		rpc_delay(task, 2 * HZ);
 		return false;
 	case -NFS4ERR_BADSLOT:
@@ -1396,14 +1396,16 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
 	}
 	trace_nfsd_cb_free_slot(task, cb);
 	nfsd41_cb_release_slot(cb);
-
-	if (RPC_SIGNALLED(task))
-		goto requeue;
-out:
 	return ret;
 retry_nowait:
-	rpc_restart_call_prepare(task);
-	goto out;
+	/*
+	 * RPC_SIGNALLED() means that the rpc_client is being torn down and
+	 * (possibly) recreated. Requeue the call in that case.
+	 */
+	if (!RPC_SIGNALLED(task)) {
+		if (rpc_restart_call_prepare(task))
+			return false;
+	}
 requeue:
 	nfsd41_cb_release_slot(cb);
 	nfsd4_requeue_cb(task, cb);