Uploading under review paper to arXiv Can I upload a paper (status: Under Review) submitted to ACM CSUR to arXiv?
Across a large part of the landscape of scholarly publications, pre-prints are (confusingly) regarded as unpublished draft versions of manuscripts that happen to circulate prior to their full-fledged publication at journals (or other outlets). It follows that to many journals &amp; publishers, it is fine to disseminate pre-prints even prior to the first submission or during the review process.
However, it seems to me that ACM follows a bit of a stricter policy. At ACM CSUR, the Author Guidelines state:

Publication, or republication, of a (perhaps revised) paper that has been widely disseminated is permitted only if the editor judges that (a) the revision contains significant amplification or clarification of the original material or (b) there is a significant additional benefit to be gained from journal publication.

With such a wording, I would be cautious, as you cannot know whether you will need to integrate major revisions or not during the review process. I would recommend you to talk to the editor directly and ask about their stance with regards to your manuscript. (Perhaps the editors are more liberal regarding pre-prints than the wording of the ACM policy on prior publications.)