Comment 7 for bug 1167622

It would appear that 9f677cf27341b7a53915ad0e018912dc022a2a24 is almost certainly the issue (based on examining the efi commits between 3.8.2 and 3.8.3). To quote its commit message:

    efi: be more paranoid about available space when creating variables

    commit 68d929862e29a8b52a7f2f2f86a0600423b093cd upstream.

    UEFI variables are typically stored in flash. For various reasons, avaiable
    space is typically not reclaimed immediately upon the deletion of a
    variable - instead, the system will garbage collect during initialisation
    after a reboot.

    Some systems appear to handle this garbage collection extremely poorly,
    failing if more than 50% of the system flash is in use. This can result in
    the machine refusing to boot. The safest thing to do for the moment is to
    forbid writes if they'd end up using more than half of the storage space.
    We can make this more finegrained later if we come up with a method for
    identifying the broken machines.

    Signed-off-by: Matthew Garrett <email address hidden>
    Cc: Josh Boyer <email address hidden>
    Signed-off-by: Matt Fleming <email address hidden>
    Signed-off-by: Greg Kroah-Hartman <email address hidden>

Which is understandable, but SERIOUSLY vulnerable to false positives.