Handle duplicate OTK uploads racing (#17241)

Currently this causes one of then to 500.

changelog.d/17241.bugfix

@@ -0,0 +1 @@
+Fix handling of duplicate concurrent uploading of device one-time-keys.

synapse/handlers/e2e_keys.py

@@ -53,6 +53,9 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 
+ONE_TIME_KEY_UPLOAD = "one_time_key_upload_lock"
+
+
 class E2eKeysHandler:
     def __init__(self, hs: "HomeServer"):
         self.config = hs.config
@@ -62,6 +65,7 @@ class E2eKeysHandler:
         self._appservice_handler = hs.get_application_service_handler()
         self.is_mine = hs.is_mine
         self.clock = hs.get_clock()
+        self._worker_lock_handler = hs.get_worker_locks_handler()
 
         federation_registry = hs.get_federation_registry()
 
@@ -855,6 +859,12 @@ class E2eKeysHandler:
     async def _upload_one_time_keys_for_user(
         self, user_id: str, device_id: str, time_now: int, one_time_keys: JsonDict
     ) -> None:
+        # We take out a lock so that we don't have to worry about a client
+        # sending duplicate requests.
+        lock_key = f"{user_id}_{device_id}"
+        async with self._worker_lock_handler.acquire_lock(
+            ONE_TIME_KEY_UPLOAD, lock_key
+        ):
             logger.info(
                 "Adding one_time_keys %r for device %r for user %r at %d",
                 one_time_keys.keys(),
@@ -893,7 +903,9 @@ class E2eKeysHandler:
                     )
 
             log_kv({"message": "Inserting new one_time_keys.", "keys": new_keys})
-        await self.store.add_e2e_one_time_keys(user_id, device_id, time_now, new_keys)
+            await self.store.add_e2e_one_time_keys(
+                user_id, device_id, time_now, new_keys
+            )
 
     async def upload_signing_keys_for_user(
         self, user_id: str, keys: JsonDict