OLPC runs / as a bind-mount for reasons explained here:
The code in umount.c (systemd-44, git as of today) currently skips bind mounts and we're not sure why.
This means that / is left mounted RW on shutdown and we experience some disk corruption here and there.
Fixed in commit 7c49259fc8f63ade6cb212a43477d7030aaaf423
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