There's a potential deadlock with the global lock and the replication lock.

dbEval grabs the Global lock first:
https://github.com/mongodb/mongo/blob/master/src/mongo/db/dbeval.cpp#L185

then the replication lock in the writeCmd called from extractWriteConcern:
https://github.com/mongodb/mongo/blob/master/src/mongo/db/repl/replication_coordinator_impl.cpp#L2604

replSetInitiate grabs the replication lock first:
https://github.com/mongodb/mongo/blob/master/src/mongo/db/repl/replication_coordinator_impl.cpp#L2094

then the global lock around here:
https://github.com/mongodb/mongo/blob/master/src/mongo/db/db_raii.cpp#L50