sub is_suffix { substr($_[0], -length($_[1])) eq $_[1] }

sub common_suffix {
    $_[0] =~ m[(?>(.+))(?(?{ not is_suffix($_[1], $^N) })(?!))]s;
    return $1;
}

##</code><code>##

use List::Util qw/ reduce /;

print reduce { common_suffix($a, $b) } qw/ redball greenball stall /;

__END__
all

##</code><code>##

sub common_suffix {
    $_[0] =~ m[
        (?>
            (.+)
        )
        (?(?{ not is_suffix($_[1], $^N) })
            (?!)
        )
    ]xs;
    return $1;
}