while these two are currently safe using synchronous mutexes we can't
easily guarantee this forever. since we have async mutexes too now we
may as well use them; the overhead they incur is small enough that we
can just ignore it here. this can be revisited later, when necessary.
Change-Id: Ia4cb2361d5638aa48e3b982a05e75ae9c4f254cd
eldritch horrors
3b9020d37c