upstream
                     /
                   /
                 /
      starting point        |
        /               upstream
   my OSX                change (1)
   config
      |       my linux
    worked    config     more stuff
     on A        |        upstream (2)
      |________ |            |
      |         |            |
      |        Merge         /|
      |  (OSX into Linux)   /
      |          |         /
    worked    worked      /     |
     on B      on C      /      |
      | ________/|   ___/    [upstream]
      |/         |  /
      |          | /
      |      Merge (upstream
   Merge C     into Linux)
  into OSX        |
    [OSX]      worked
                on D
                  |
               worked
                on E
               [Linux]