Implement cancellation support/protection for module callbacks (#12568)

There's no guarantee that module callbacks will handle cancellation
appropriately. Protect module callbacks with read semantics from
cancellation and avoid swallowing `CancelledError`s that arise.

Other module callbacks, such as the `on_*` callbacks, are presumed to
live on code paths that involve writes and aren't cancellation-friendly.
These module callbacks have been left alone.

Signed-off-by: Sean Quah <seanq@element.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/synapse/handlers/account_validity.py b/synapse/handlers/account_validity.py
index 05a138410e..33e45e3a11 100644
--- a/synapse/handlers/account_validity.py
+++ b/synapse/handlers/account_validity.py
@@ -23,6 +23,7 @@ from synapse.api.errors import AuthError, StoreError, SynapseError
 from synapse.metrics.background_process_metrics import wrap_as_background_process
 from synapse.types import UserID
 from synapse.util import stringutils
+from synapse.util.async_helpers import delay_cancellation
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -150,7 +151,7 @@ class AccountValidityHandler:
             Whether the user has expired.
         """
         for callback in self._is_user_expired_callbacks:
-            expired = await callback(user_id)
+            expired = await delay_cancellation(callback(user_id))
             if expired is not None:
                 return expired