I would say that the task of detecting circular references in a data structure does not involve sorting at all. Simply walk the data structure/hierarchy/whatever while keeping track of the path you followed to get there.

Here's some untested code to show what I mean:

sub is_circular {
  my $obj = shift; # Object to be traversed
  my $path = shift || [];

  # Check of $obj is in the $path
  foreach my $ancestor (@{$path}) {
    return 1 if $ancestor eq $obj;
  }

  # Check the children recursively, depth first
  # (My imaginary $obj conveniently has 
  # a method for getting an array of its children)
  foreach my $child ($obj->children) {
    return 1 if is_circular($child, [ @{$path}, $obj ] );
  }

  return 0;
}
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This can be done recursively or in a linear fashion if this suits you better. Modules already exist but writing your own code would probably be faster than trying to fit an existing module with your particular data.