PYTHON-4019 Infinite loop in generic transactional provider due to dup keys

Author: blink1073

pymongo/asynchronous/client_session.py

@@ -660,6 +660,11 @@ async def callback(session, custom_arg, custom_kwarg=None):
         ``with_transaction`` starts a new transaction and re-executes
         the ``callback``.
 
+        The ``callback`` MUST NOT silently handle command errors
+        without allowing such errors to propagate. Command errors may abort the
+        transaction on the server, and an attempt to commit the transaction will
+        be rejected with a ``NoSuchTransaction`` error.
+
         When :meth:`~AsyncClientSession.commit_transaction` raises an exception with
         the ``"UnknownTransactionCommitResult"`` error label,
         ``with_transaction`` retries the commit until the result of the

pymongo/synchronous/client_session.py

@@ -659,6 +659,11 @@ def callback(session, custom_arg, custom_kwarg=None):
         ``with_transaction`` starts a new transaction and re-executes
         the ``callback``.
 
+        The ``callback`` MUST NOT silently handle command errors
+        without allowing such errors to propagate. Command errors may abort the
+        transaction on the server, and an attempt to commit the transaction will
+        be rejected with a ``NoSuchTransaction`` error.
+
         When :meth:`~ClientSession.commit_transaction` raises an exception with
         the ``"UnknownTransactionCommitResult"`` error label,
         ``with_transaction`` retries the commit until the result of the