drop2.js tests the ability to drop a collection while a long running read operation is occurring on that same collection.

Unfortunately, it does this using a count given a "$where: while(1) sleep;" operation. Normally, this works okay, but if you are using auth, an extra read lock is necessary to authenticate the operations. This extra read lock in combination with the journal thread doing a commit may deadlock against the read lock held by the count query.
To fix this, I am adding drop2.js to the auth testing blacklist.