ostree-remount.service fails on Rpi4

[dustymabe]

Not sure why it fails, but it does pretty consistently:

× ostree-remount.service - OSTree Remount OS/ Bind Mounts
     Loaded: loaded (/usr/lib/systemd/system/ostree-remount.service; enabled; vendor preset: enabled)
     Active: failed (Result: exit-code) since Tue 2021-05-25 11:19:26 UTC; 1min 41s ago
       Docs: man:ostree(1)
    Process: 954 ExecStart=/usr/lib/ostree/ostree-remount (code=exited, status=1/FAILURE)
   Main PID: 954 (code=exited, status=1/FAILURE)
        CPU: 12ms

May 25 11:19:26 rpi4 systemd[1]: Starting OSTree Remount OS/ Bind Mounts...
May 25 11:19:26 rpi4 ostree-remount[954]: ostree-remount: failed to remount(ro) /sysroot: Device or resource busy
May 25 11:19:26 rpi4 systemd[1]: ostree-remount.service: Main process exited, code=exited, status=1/FAILURE
May 25 11:19:26 rpi4 systemd[1]: ostree-remount.service: Failed with result 'exit-code'.
May 25 11:19:26 rpi4 systemd[1]: Failed to start OSTree Remount OS/ Bind Mounts.
May 25 11:19:26 rpi4 systemd[1]: ostree-remount.service: Triggering OnFailure= dependencies.

See attached journal.txt for more info.

The config I'm using though I don't think it has anything to do with the issue as I think it was having the same problem before I started doing any partitioning:

$ cat pi.bu
variant: fcos
version: 1.4.0-experimental
storage:
  disks:
    - device: /dev/disk/by-id/usb-WD_My_Passport_2627_575841324142304334333839-0:0
      wipe_table: false
      partitions:
        - number: 4
          label: root
          size_mib: 51200
          resize: true
        - number: 5
          label: var-home
          size_mib: 102400
  filesystems:
    - path: /var/home
      device: /dev/disk/by-partlabel/var-home
      format: xfs
      wipe_filesystem: false
      label: var-home
      with_mount_unit: true
  files:
    - path: /etc/hostname
      mode: 0644
      contents:
        inline: rpi4
    - path: /etc/systemd/zram-generator.conf
      mode: 0644
      contents:
        inline: |
          # This config file enables a /dev/zram0 device with the default settings
          [zram0]

[cgwalters]

See also ostreedev/ostree#2187

[jlebon]

This also looks like the same issue as #746.