There is a reachable deadlock condition between the db mutex and js mutex, which has been seen in v8 (SERVER-1756). The same issue may affect spidermonkey, as a spidermonkey mutex guards all sm calls.

To fix, all javascript calls from c++ must occur while a db mutex is held. In the diagnosed case, javascript calls within MRState::MRState() were made without a db mutex. These calls held the v8 mutex and requested the db mutex, while a concurrent db.eval held the db mutex and requested the v8 mutex.