From 49a683d871add82fb1a8125c6803ac15ec7d341b Mon Sep 17 00:00:00 2001
From: Sean Quah <8349537+squahtx@users.noreply.github.com>
Date: Fri, 8 Oct 2021 12:27:16 +0100
Subject: [PATCH] Fix long-standing bug where `ReadWriteLock` could drop
logging contexts (#10993)
Use `PreserveLoggingContext()` to ensure that logging contexts are not
lost when exiting a read/write lock.
When exiting a read/write lock, callbacks on a `Deferred` are triggered
as a signal to any waiting coroutines. Any waiting coroutine that
becomes runnable is likely to follow the Synapse logging context rules
and will restore its own logging context, then either run to completion
or await another `Deferred`, resetting the logging context in the
process.
---
changelog.d/10993.misc | 1 +
synapse/util/async_helpers.py | 6 ++++--
2 files changed, 5 insertions(+), 2 deletions(-)
create mode 100644 changelog.d/10993.misc
diff --git a/changelog.d/10993.misc b/changelog.d/10993.misc
new file mode 100644
index 0000000000..23c73dbac5
--- /dev/null
+++ b/changelog.d/10993.misc
@@ -0,0 +1 @@
+Fix a long-standing bug where `ReadWriteLock`s could drop logging contexts on exit.
diff --git a/synapse/util/async_helpers.py b/synapse/util/async_helpers.py
index 82d918a05f..5df80ea8e7 100644
--- a/synapse/util/async_helpers.py
+++ b/synapse/util/async_helpers.py
@@ -438,7 +438,8 @@ class ReadWriteLock:
try:
yield
finally:
- new_defer.callback(None)
+ with PreserveLoggingContext():
+ new_defer.callback(None)
self.key_to_current_readers.get(key, set()).discard(new_defer)
return _ctx_manager()
@@ -466,7 +467,8 @@ class ReadWriteLock:
try:
yield
finally:
- new_defer.callback(None)
+ with PreserveLoggingContext():
+ new_defer.callback(None)
if self.key_to_current_writer[key] == new_defer:
self.key_to_current_writer.pop(key)
--
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