From 31c79d5b34422d033531fcaee343cffa4e42475a Mon Sep 17 00:00:00 2001
From: David Robertson <davidr@element.io>
Date: Tue, 26 Apr 2022 15:00:36 +0100
Subject: [PATCH 1/2] Comment out dodgy `log_kv`

Mitigation for #12552.
---
 synapse/handlers/device.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 3c0fc756d46b..319836da2bee 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -683,9 +683,12 @@ async def _handle_new_device_update_async(self) -> None:
                             self.federation_sender.send_device_messages(
                                 host, immediate=False
                             )
-                            log_kv(
-                                {"message": "sent device update to host", "host": host}
-                            )
+                            # TODO: when called, this isn't in a logging context.
+                            # This leads to log spam, sentry event spam, and massive
+                            # memory usage. See #12552.
+                            # log_kv(
+                            #     {"message": "sent device update to host", "host": host}
+                            # )
 
                     if current_stream_id != stream_id:
                         # Clear the set of hosts we've already sent to as we're

From fb5ced47707f812c4374bbf367ad8844aad55c1e Mon Sep 17 00:00:00 2001
From: David Robertson <davidr@element.io>
Date: Tue, 26 Apr 2022 15:05:11 +0100
Subject: [PATCH 2/2] Changelog

---
 changelog.d/12554.bugfix | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/12554.bugfix

diff --git a/changelog.d/12554.bugfix b/changelog.d/12554.bugfix
new file mode 100644
index 000000000000..48c1146db52b
--- /dev/null
+++ b/changelog.d/12554.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in Synapse 1.58.0rc1 where the main process could consume excessive amounts of CPU and memory handling sentry logging failures.