From 693156aaf4579f48ad265f42f90b1bd73feda129 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 3 Oct 2019 17:33:54 +0100
Subject: [PATCH 1/4] Don't regenerate numeric user ID if registration fails.

This causes huge amounts of DB IO if registrations start to fail e.g.
because the DB is struggling with IO.
---
 synapse/handlers/register.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index 06bd03b77..6dd7ef374 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -220,7 +220,7 @@ class RegistrationHandler(BaseHandler):
             attempts = 0
             user = None
             while not user:
-                localpart = yield self._generate_user_id(attempts > 0)
+                localpart = yield self._generate_user_id()
                 user = UserID(localpart, self.hs.hostname)
                 user_id = user.to_string()
                 yield self.check_user_id_not_appservice_exclusive(user_id)
@@ -379,10 +379,10 @@ class RegistrationHandler(BaseHandler):
                 )
 
     @defer.inlineCallbacks
-    def _generate_user_id(self, reseed=False):
-        if reseed or self._next_generated_user_id is None:
+    def _generate_user_id(self):
+        if self._next_generated_user_id is None:
             with (yield self._generate_user_id_linearizer.queue(())):
-                if reseed or self._next_generated_user_id is None:
+                if self._next_generated_user_id is None:
                     self._next_generated_user_id = (
                         yield self.store.find_next_generated_user_id_localpart()
                     )

From 4fc60f12deef19407e9b761f3d9c24c48384118c Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 3 Oct 2019 17:35:50 +0100
Subject: [PATCH 2/4] Newsfile

---
 changelog.d/6161.misc | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/6161.misc

diff --git a/changelog.d/6161.misc b/changelog.d/6161.misc
new file mode 100644
index 000000000..7c5d61cb8
--- /dev/null
+++ b/changelog.d/6161.misc
@@ -0,0 +1 @@
+Don't regenerate numeric user ID if registration fails.

From ab8a64772b9e663e74fbdafef9a729bd49369e65 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 3 Oct 2019 17:42:32 +0100
Subject: [PATCH 3/4] Remove unused variable

---
 synapse/handlers/register.py | 2 --
 1 file changed, 2 deletions(-)

diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index 6dd7ef374..53410f120 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -217,7 +217,6 @@ class RegistrationHandler(BaseHandler):
 
         else:
             # autogen a sequential user ID
-            attempts = 0
             user = None
             while not user:
                 localpart = yield self._generate_user_id()
@@ -238,7 +237,6 @@ class RegistrationHandler(BaseHandler):
                     # if user id is taken, just generate another
                     user = None
                     user_id = None
-                    attempts += 1
 
         if not self.hs.config.user_consent_at_registration:
             yield self._auto_join_rooms(user_id)

From 0186ec9df7e55e35fa9b6579869cd308dc178a3c Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 3 Oct 2019 17:46:43 +0100
Subject: [PATCH 4/4] Fixup newsfile

---
 changelog.d/6161.bugfix | 1 +
 changelog.d/6161.misc   | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)
 create mode 100644 changelog.d/6161.bugfix
 delete mode 100644 changelog.d/6161.misc

diff --git a/changelog.d/6161.bugfix b/changelog.d/6161.bugfix
new file mode 100644
index 000000000..a0e2adb97
--- /dev/null
+++ b/changelog.d/6161.bugfix
@@ -0,0 +1 @@
+Fix bug where guest account registration can wedge after restart.
diff --git a/changelog.d/6161.misc b/changelog.d/6161.misc
deleted file mode 100644
index 7c5d61cb8..000000000
--- a/changelog.d/6161.misc
+++ /dev/null
@@ -1 +0,0 @@
-Don't regenerate numeric user ID if registration fails.