Fix a race when registering via email 3pid #16827
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MatMaul
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Jan 18, 2024
| @@ -506,6 +509,23 @@ async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]: | |||
| "An access token should not be provided on requests to /register (except if type is m.login.application_service)", | |||
| ) | |||
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| # Take a global lock when doing user registration to avoid races, | |||
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I am only protecting normal user registration with the lock because I think _do_appservice_registration and _do_guest_registration are safe but I am not sure to be honest, especially for the appservice one.
Out of safety we may protect the whole code in on_POST, opinions welcome.
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Failing tests should turn to green once #16840 is merged. |
erikjohnston
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When a lot of locks are waiting for a single lock, notifying all locks independently with `call_later` on each release is really costly and incurs some kind of async contention, where the CPU is spinning a lot for not much. The included test is taking around 30s before the change, and 0.5s after. It was found following failing tests with #16827.
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When hitting the race, 2 different users are created for an unique 3pid email.
Performance impact should be fairly minimal since we usually don't register a new user 10 times per second, unlike sending messages.
Pull Request Checklist
EventStoretoEventWorkerStore.".code blocks.(run the linters)