What you *could* do is to start putting processes to sleep if they
attempt to write to the frozen filesystem, and then detect the
deadlock case where the process holding the file descriptor used to
freeze the filesystem gets frozen because it attempted to write to the
filesystem --- at which point it gets some kind of signal (which
defaults to killing the process), and the filesystem is unfrozen and
as part of the unfreeze you wake up all of the processes that were put
to sleep for touching the frozen filesystem.