util-linux 2.39 regression: overlayfs root fails to remount ro

[sdbtools]

Steps to reproduce:

sudo ./build-x86-images.sh -- -v linux6.7

Result:

Writing to 'stdio:void-live-x86_64-20240222-base.iso' completed successfully.

Created /xxx/void-mklive/void-live-x86_64-20240222-base.iso (1.1G) successfully.
umount: /xxx/void-mklive/tmp.t1PsYOZ1A5/image/rootfs/sys: not found
ERROR: failed to unmount /xxx/void-mklive/tmp.t1PsYOZ1A5/image/rootfs/sys/

Version:

$ ./build-x86-images.sh -V
build-x86-images.sh 0.25 63c1152

I cannot boot created ISO (kernel 6.7.5). rootfs won't mount.

[classabbyamp]

the error during image generation itself is spurious, that's just a missing check in the cleanup (9708d22)

can't repro the mount failure with images generated on 2024-02-17

can repro the mount failure with an image on 6.6 generated today (make live-iso-all LIVE_ARCHS="x86_64" LIVE_FLAVORS="base")

the most probable cause is either the util-linux update or the kernel update, IMO

[classabbyamp]

can confirm, reverting the latest util-linux and util-linux-common updates fixed it

[classabbyamp]

for future reference, the exact error is:

=> Remounting rootfs read-only...
mount: /: mount point not mounted or bad option.
       dmesg(1) may have more information after failed mount system call.

what's failing appears to be mount -o remount,ro / in /etc/runit/core-services/03-filesystems.sh

[classabbyamp]

the issue appears to be: util-linux/util-linux#2528 (comment)

from the util-linux relnotes:

• supports new file descriptors based mount kernel API. This change is
  very aggressive to libmount code, but hopefully, it does not introduce
  regressions in traditional mount(8) behavior. The library is still backward
  compatible with old kernels and can fall back to classic mount(2) API
  if necessary. The old mount(2) is also used for btrfs when used with SELinux
  context= mount options because the btrfs kernel driver does not support this
  use-case yet; we may see the more in-kernel issue... Use
  --disable-libmount-mountfd-support to disable this feature.