This is the upstream EL8 squashfs-tools 4.3-19.el8 patched with:
https://github.com/plougher/squashfs-tools/commit/de03266983ceb62e5365aac84fcd3b2fd4d16e6f
To fix:
https://bugzilla.redhat.com/show_bug.cgi?id=1785652
It is needed to avoid sporadic rare failures of mksquashfs in Singularity testing on large multi-core machines where a very large number of mksquashfs runs take place during make e2e-test.