Do editors need all reviewers to be unanimous in their decision before acceptance? Assume an editor has sent out a manuscript to reviewers.  Let's say the manuscript has potential but with mixed reviews; some reviewers say accept whilst others recommend revision/reject.  The editor recommends re-submission.  So the manuscript goes through the usual revision-resubmission-revision-... process.

As an editor, does he/she need to all reviewers to be thoroughly happy before accepting the manuscript? Can he/she accept/reject the manuscript based on the majority rule?

Note, some journals have a limit on the maximum number of re-submissions, meaning the re-submission process cannot continue forever.
First of all, reviewers give a recommendation. It is the editor who makes the final decision.

It is possible to have an editor going against the reviewers opinion.
An example is this article.
It is open peer-review, so you can read the reviews and the answer of the editor. He says in his comment:


  I decided to continue the review process even though 2 of the 3 reviews recommend rejection.


So the answer is no, an editor does not need to receive unanimous recommendations from the reviewers to make a decision.