Block concurrent pipeline processings

CHANGELOG

@@ -54,13 +54,11 @@ v 8.12.0 (unreleased)
 v 8.11.4 (unreleased)
   - Fix broken gitlab:backup:restore because of bad permissions on repo storage !6098 (Dirk Hörner)
   - Creating an issue through our API now emails label subscribers !5720
+  - Block concurrent updates for Pipeline
   - Fix resolving conflicts on forks
   - Fix diff commenting on merge requests created prior to 8.10
-
-v 8.11.4 (unreleased)
   - Fix issue boards leak private label names and descriptions
 
-v 8.11.3 (unreleased)
 v 8.11.3
   - Do not enforce using hash with hidden key in CI configuration. !6079
   - Allow system info page to handle case where info is unavailable

app/services/ci/process_pipeline_service.rb

@@ -10,13 +10,15 @@ module Ci
         create_builds!
       end
 
-      new_builds =
-        stage_indexes_of_created_builds.map do |index|
-          process_stage(index)
-        end
+      @pipeline.with_lock do
+        new_builds =
+          stage_indexes_of_created_builds.map do |index|
+            process_stage(index)
+          end
 
-      # Return a flag if a when builds got enqueued
-      new_builds.flatten.any?
+        # Return a flag if a when builds got enqueued
+        new_builds.flatten.any?
+      end
     end
 
     private