Update comments for getting and removing loopback device at iSCSI,FC,RBD

pkg/volume/fc/fc_util.go

@@ -348,6 +348,11 @@ func (util *FCUtil) DetachBlockFCDisk(c fcDiskUnmapper, mapPath, devicePath stri
 	glog.V(4).Infof("fc: find destination device path from symlink: %v", dstPath)
 
 	// Get loopback device which takes fd lock for device beofore detaching a volume from node.
+	// TODO: This is a workaround for issue #54108
+	// Currently local attach plugins such as FC, iSCSI, RBD can't obtain devicePath during
+	// GenerateUnmapDeviceFunc() in operation_generator. As a result, these plugins fail to get
+	// and remove loopback device then it will be remained on kubelet node. To avoid the problem,
+	// local attach plugins needs to remove loopback device during TearDownDevice().
 	var devices []string
 	blkUtil := volumeutil.NewBlockVolumePathHandler()
 	dm := c.deviceUtil.FindMultipathDeviceForDevice(dstPath)

pkg/volume/iscsi/iscsi_util.go

@@ -512,8 +512,12 @@ func (util *ISCSIUtil) DetachBlockISCSIDisk(c iscsiDiskUnmapper, mapPath string)
 	if mappedDevicePath := c.deviceUtil.FindMultipathDeviceForDevice(devicePath); mappedDevicePath != "" {
 		devicePath = mappedDevicePath
 	}
-	// Get loopback device which takes fd lock for devicePath before
-	// detaching a volume from node.
+	// Get loopback device which takes fd lock for devicePath before detaching a volume from node.
+	// TODO: This is a workaround for issue #54108
+	// Currently local attach plugins such as FC, iSCSI, RBD can't obtain devicePath during
+	// GenerateUnmapDeviceFunc() in operation_generator. As a result, these plugins fail to get
+	// and remove loopback device then it will be remained on kubelet node. To avoid the problem,
+	// local attach plugins needs to remove loopback device during TearDownDevice().
 	blkUtil := volumeutil.NewBlockVolumePathHandler()
 	loop, err := volumeutil.BlockVolumePathHandler.GetLoopDevice(blkUtil, devicePath)
 	if err != nil {

pkg/volume/rbd/rbd.go

@@ -921,6 +921,12 @@ func (rbd *rbdDiskUnmapper) TearDownDevice(mapPath, _ string) error {
 	if err != nil {
 		return fmt.Errorf("rbd: failed to get loopback for device: %v, err: %v", device, err)
 	}
+	// Get loopback device which takes fd lock for device beofore detaching a volume from node.
+	// TODO: This is a workaround for issue #54108
+	// Currently local attach plugins such as FC, iSCSI, RBD can't obtain devicePath during
+	// GenerateUnmapDeviceFunc() in operation_generator. As a result, these plugins fail to get
+	// and remove loopback device then it will be remained on kubelet node. To avoid the problem,
+	// local attach plugins needs to remove loopback device during TearDownDevice().
 	blkUtil := volutil.NewBlockVolumePathHandler()
 	loop, err := volutil.BlockVolumePathHandler.GetLoopDevice(blkUtil, device)
 	if err != nil {