Want to get rid of all those unread messages in Gmail? Or, just like me, have some unread messages you can't find and want to reset the unread count to zero? Well, here is the solution:
Type "is:unread" in the search bar. Then select "Unread" as seen in the picture below.
In the "More actions" dropdown select "Mark as read".
And that's it. Your inbox shouldn't be reporting any unread messages by now.