From 104fdaf4464101ff1f7e3112f6874e9d12b755f6 Mon Sep 17 00:00:00 2001
From: Eugen Rochko <eugen@zeonfederated.com>
Date: Thu, 26 May 2022 18:58:19 +0200
Subject: [PATCH] Fix concurrent unfollowing decrementing follower count more
 than once

---
 app/services/unfollow_service.rb | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/app/services/unfollow_service.rb b/app/services/unfollow_service.rb
index 151f3674f..0f04713d1 100644
--- a/app/services/unfollow_service.rb
+++ b/app/services/unfollow_service.rb
@@ -13,7 +13,13 @@ class UnfollowService < BaseService
     @target_account = target_account
     @options        = options
 
-    unfollow! || undo_follow_request!
+    RedisLock.acquire(redis: Redis.current, key: "relationship:#{[source_account.id, target_account.id].sort.join(':')}", autorelease: 90.seconds) do |lock|
+      if lock.acquired?
+        unfollow! || undo_follow_request!
+      else
+        raise Mastodon::RaceConditionError
+      end
+    end
   end
 
   private