无法写入EMMC，提示无法卸载分区

[rule2c]

AMLOGIC_SOC Value[ s905d ]
FDTFILE Value [meson-gxl-s905d-phicomm-n1.dtb ]
MAINLINE UBOOT Value []UBOOT_OVERLOAD Value [u-boot-n1.bin ]
K510[0]
ANDROID_UBooT Value [/lib/u-boot/u-boot-2015-phicomm-n1.bin ]
/mnt/mmcblk2p4 umount -f
/mnt/mmcblk2p4 umount: /mnt/mmcblk2p4: target is busy.
/mnt/mmcblk2p4 Cannot be uninstalled, the installation process is aborted.

求大佬指点，谢谢。