fix: NodeUnpublishVolume should be idempotent

In case the NodeUnpublishVolume procedure was aborted after unmounting
the volume, a repeated call will return an error like "Volume not
mounted".

Instead of returning the error, log a message and return success to
indicate that the volume is not mounted anymore.

Author: nixpanic

pkg/nfs/nodeserver.go

@@ -139,7 +139,8 @@ func (ns *NodeServer) NodeUnpublishVolume(ctx context.Context, req *csi.NodeUnpu
 		return nil, status.Error(codes.Internal, err.Error())
 	}
 	if notMnt {
-		return nil, status.Error(codes.NotFound, "Volume not mounted")
+		klog.V(2).Infof("NodeUnpublishVolume: Targetpath %s of volumeID(%s) is not mounted", targetPath, volumeID)
+		return &csi.NodeUnpublishVolumeResponse{}, nil
 	}
 
 	klog.V(2).Infof("NodeUnpublishVolume: CleanupMountPoint %s on volumeID(%s)", targetPath, volumeID)

pkg/nfs/nodeserver_test.go

@@ -189,9 +189,8 @@ func TestNodeUnpublishVolume(t *testing.T) {
 			expectedErr: status.Error(codes.Internal, "fake IsLikelyNotMountPoint: fake error"),
 		},
 		{
-			desc:        "[Error] Volume not mounted",
-			req:         csi.NodeUnpublishVolumeRequest{TargetPath: targetFile, VolumeId: "vol_1"},
-			expectedErr: status.Error(codes.NotFound, "Volume not mounted"),
+			desc: "[Success] Volume not mounted",
+			req:  csi.NodeUnpublishVolumeRequest{TargetPath: targetFile, VolumeId: "vol_1"},
 		},
 	}