First I thought it's strange that there's no link to a bug tracker on the OpenJDK project page, then I found bugs.openjdk.java.net, but it's only for accredited project members. How do people outside the ivory tower contribute issues? There's the mailing list and some people call sending issues and patches to a mailing list bug tracking... but the development and usage of bug tracker contradicts.
Go to http://bugs.java.com or jump straight to the report page: http://bugreport.java.com/
My interpretation of their FAQ is that this will be triaged by an Oracle engineer, and if accepted it will be assigned a number and (usually) become visible in both Oracles + the OpenJDK bug databases.
It would be really helpful if this info/link were on the OpenJDK bug page too. The database split is already confusing enough - when your goal is to contribute to OpenJDK but you find yourself at an Oracle-branded page, it seems like you've gone to the wrong place.
UDPATE (Nov 2019): To add Additional information to a bug (FAQ point 6):
File a new incident with the subject line "Additional information to JDK-XXXXXXX'. Replace XXXXXXX with the reference number received when the report is filed. We are working on a system where you will be able to provide additional information to the existing bug.
Now, if you're curious who can get direct access to the bug database...
From (https://bugs.openjdk.java.net/):
Everyone with OpenJDK Author status or above has a [JDK Bug System] account which may be used to create and edit bugs. Those without accounts can view bugs anonymously.
To understand that, you need to navigate the various "role" definitions:
http://openjdk.java.net/bylaws#author
From Section 7:
An Author for a Project is a Contributor who has been granted the right to create changesets intended to be pushed into a specific Project’s code repositories, but does not have the right to push such changesets directly.
From Section 2:
A Contributor is a Participant who has signed the Oracle Contributor Agreement (OCA), or who works for an organization that has signed that agreement or its equivalent and makes contributions within the scope of that work and subject to that agreement. A Contributor may submit changes larger than a simple patch, may propose new Projects, and may take on various roles within Groups and Projects.
and ...
A Participant is an individual who has subscribed to one or more OpenJDK mailing lists. A Participant may post messages to a list, submit simple patches, and make other kinds of small contributions.
So the bar is set pretty high. :-/