Kernel-4.14: With ubuntu-18.04 building rootfs images and booting gives SQUASHFS error: xz decompression failed, data probably corrupt

[Pintu Agarwal]

Hi,
Here are few details.
* Linux Kernel: 4.14
* Processor: Qualcomm Arm32 Cortex-A7
* Storage: NAND 512MB
* Platform: Simple busybox
* Filesystem: UBIFS, Squashfs
* Build system: Linux Ubuntu 18.04 with Yocto build system
* Consists of nand raw partitions, squashfs ubi volumes.

What we are trying to do:
We are trying to boot dm-verity enabled rootfs on our system.
The images for rootfs were generated on Ubuntu 18.04 machine using
Yocto build system.

Issue:
Earlier, when we were using Ubuntu 16.04 to generate our images, the
system was booting fine even with dm-verity enabled.
Recently we switched to Ubuntu 18.04 build machine, and now with the
same changes we are seeing the below squashfs error, just after the
mount.
Note: with 18.04 also our rootfs is mounting successfully and
dm-verity is also working fine.
We only get these squashfs errors flooded in the boot logs:
{{{
....
[    5.153479] device-mapper: init: dm-0 is ready
[    5.334282] VFS: Mounted root (squashfs filesystem) readonly on device 253:0.
....
[    8.954120] SQUASHFS error: xz decompression failed, data probably corrupt
[    8.954153] SQUASHFS error: squashfs_read_data failed to read block 0x1106
[    8.970316] SQUASHFS error: Unable to read data cache entry [1106]
[    8.970349] SQUASHFS error: Unable to read page, block 1106, size 776c
[    8.980298] SQUASHFS error: Unable to read data cache entry [1106]
[    8.981911] SQUASHFS error: Unable to read page, block 1106, size 776c
[    8.988280] SQUASHFS error: Unable to read data cache entry [1106]
....
}}}

Note: For dm-verity wwe are trying to append the verity-metadata as
part of our rootfs image like this:
...
218 +    with open(verity_md_img, "rb") as input_file:
219 +        with open(sparse_img, "ab") as out_file:
220 +            for line in input_file:
221 +                out_file.write(line)
....

These changes work fine when we build it with Ubuntu 16.04.
So, we are wondering what could be the issue with Ubuntu 18.04 build ?

If there is any history about it please let us know.


Regards,
Pintu