If the ext4 rootfs on your on board storage is damaged due to sudden loose power or other reasons. You need to recovery the file system.
The message is like below:
Message: [ 78.110021] EXT4-fs error (device mtdblock1): ext4_mb_generate_buddy:736: group 42, 6555 blocks in bitmap, 6556 in gd
To recovery the rootfs on nand, you need to boot the rootfs from another media such as usb hard drive or sdcard. Please check the instructions boot linux from uSD card.
After booting rootfs from uSD card or USB driver, you can access the Nand rootfs by /dev/mtdblock1, use fsck.ext4 to check the rootfs.