I've been debugging a cause of flakey complement-crypto tests for
about a month now. I was pretty convinced it was deadlocking
somewhere in the memory store `save_changes` code. With additional
logging, it's now clear that the there is an ABBA style deadlock
when `save_changes` is called at the same time as `get_state_events`.
I've also adjusted code for `get_user_ids` as it has a very similar
pattern and also acquires locks in reverse order to `save_changes`,
so is potentially vulnerable to this.
Kegan Dougal
e5f92947e7