Permit concurrent loads in gpg keychain mutex

changelogs/unreleased/rails5-gpg-permit-concurrent.yml

+---
+title: Permit concurrent loads in gpg keychain mutex
+merge_request: 20894
+author: Jasper Maes
+type: fixed

lib/gitlab/gpg.rb

@@ -71,10 +71,18 @@ module Gitlab
       if MUTEX.locked? && MUTEX.owned?
         optimistic_using_tmp_keychain(&block)
       else
+        if Gitlab.rails5?
+          ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
             MUTEX.synchronize do
               optimistic_using_tmp_keychain(&block)
             end
           end
+        else
+          MUTEX.synchronize do
+            optimistic_using_tmp_keychain(&block)
+          end
+        end
+      end
     end
 
     # 1. Returns the custom home directory if one has been set by calling