Filesystem is sometimes mounted incorrectly and fails to boot

[NeroReflex]

Starting from 6.8 kernel we begun observing that the boot may fail to enter game mode because lots of services failed to start.

I investigated and every failed service failed because either /etc or /var was read-only.

If one reads /etc/fstab it will be clear that those are intended to be mounted as RW, but this is not what happens.

Instead btrfs share mount flags across everything from the same filesystem, in /etc/fstab / is re-mounted (after starting systemd) as RO and such mount is started in parallel with others 3 mounts (that are RW).

The first successful mount determines if /frzr_root and /var and /etc will be RO or RW.

Chances are 3/4 to mount the filesystem correctly and 1/4 of mounting the whole filesystem as RO.

Relevant btrfs documentation is here first blue box in that page reads "Most mount options apply to the whole filesystem and only options in the first mounted subvolume will take effect".