Is it really Rashi?

Among the many commentaries on Pirkei Avot is one that is attributed to Rashi.  Some people are surprised to note that, while Rashi's commentaries on Tanach and the Gemara are pretty well indispensable and are found in more or less every modern printed edition of those basic works, it is not the commentary of Rashi but that of Rabbi Ovadya Bartenura which occupies the "inner track" of the printed page. The Rashi commentary is found in numerous editions, but it is clearly held in lower esteem than that of the Bartenura since it is far less often cited or turned to for guidance.

I recall that at least one major rabbinical scholar -- Rabbi Yaakov Emden -- has opined that the Rashi commentary on Avot is not by Rashi at all but has been attributed to him.  I also recall that some other scholars have taken the opposite view and have defended Rashi's authorship, some with considerable passion.  Unfortunately, when I first came across this issue I did not make note of the various contributors to this debate or to the mishnayot that generated their opinions that the Rashi was genuine or not.  

If any readers can enlighten me by posting as comments below any references to those who hold that the Rashi commentary is authentic or otherwise, I should be hugely grateful. Thanks!