my (@match) = $str =~ /(?:^foo (?=(?:m \d+ )+bar)|(?<!^)\G)m (\d+) /g;

##</code><code>##

my (@match) = $str =~
  / (?: ^foo\ (?= (?:m\ \d+\ )+bar) # overall match from ^foo
      | (?<!^) \G                   # or continue from not-^
    )
    m\ (\d+)\                       # grab each digit sequence
  /xg;