Fix deadlock in backup repositories rake task

changelogs/unreleased/fix_concurrent_backup.yml

+---
+title: Fix deadlock in backup repositories rake task
+merge_request: 41042
+author:
+type: fixed

lib/backup/repository.rb

@@ -148,20 +148,22 @@ module Backup
     private
 
     def dump_consecutive
-      Project.find_each(batch_size: 1000) do |project|
+      Project.includes(:route).find_each(batch_size: 1000) do |project|
         dump_project(project)
       end
     end
 
     def dump_storage(storage, semaphore, max_storage_concurrency:)
       errors = Queue.new
-      queue = SizedQueue.new(1)
+      queue = InterlockSizedQueue.new(1)
 
       threads = Array.new(max_storage_concurrency) do
         Thread.new do
           Rails.application.executor.wrap do
             while project = queue.pop
-              semaphore.acquire
+              ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+                semaphore.acquire
+              end
 
               begin
                 dump_project(project)
@@ -176,7 +178,7 @@ module Backup
         end
       end
 
-      Project.for_repository_storage(storage).find_each(batch_size: 100) do |project|
+      Project.for_repository_storage(storage).includes(:route).find_each(batch_size: 100) do |project|
         break unless errors.empty?
 
         queue.push(project)
@@ -241,5 +243,23 @@ module Backup
         pool.schedule
       end
     end
+
+    class InterlockSizedQueue < SizedQueue
+      extend ::Gitlab::Utils::Override
+
+      override :pop
+      def pop(*)
+        ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+          super
+        end
+      end
+
+      override :push
+      def push(*)
+        ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+          super
+        end
+      end
+    end
   end
 end

spec/lib/backup/repository_spec.rb

@@ -47,15 +47,27 @@ RSpec.describe Backup::Repository do
         end
 
         it 'project query raises an error' do
-          allow(Project).to receive(:find_each).and_raise(ActiveRecord::StatementTimeout)
+          allow(Project).to receive_message_chain(:includes, :find_each).and_raise(ActiveRecord::StatementTimeout)
 
           expect { subject.dump(max_concurrency: 1, max_storage_concurrency: 1) }.to raise_error(ActiveRecord::StatementTimeout)
         end
       end
+
+      it 'avoids N+1 database queries' do
+        control_count = ActiveRecord::QueryRecorder.new do
+          subject.dump(max_concurrency: 1, max_storage_concurrency: 1)
+        end.count
+
+        create_list(:project, 2, :wiki_repo)
+
+        expect do
+          subject.dump(max_concurrency: 1, max_storage_concurrency: 1)
+        end.not_to exceed_query_limit(control_count)
+      end
     end
 
     [4, 10].each do |max_storage_concurrency|
-      context "max_storage_concurrency #{max_storage_concurrency}", quarantine: 'https://gitlab.com/gitlab-org/gitlab/-/issues/241701' do
+      context "max_storage_concurrency #{max_storage_concurrency}" do
         it 'creates the expected number of threads' do
           expect(Thread).to receive(:new)
             .exactly(storage_keys.length * (max_storage_concurrency + 1)).times
@@ -89,7 +101,7 @@ RSpec.describe Backup::Repository do
           end
 
           it 'project query raises an error' do
-            allow(Project).to receive_message_chain('for_repository_storage.find_each').and_raise(ActiveRecord::StatementTimeout)
+            allow(Project).to receive_message_chain(:for_repository_storage, :includes, :find_each).and_raise(ActiveRecord::StatementTimeout)
 
             expect { subject.dump(max_concurrency: 1, max_storage_concurrency: max_storage_concurrency) }.to raise_error(ActiveRecord::StatementTimeout)
           end
@@ -102,6 +114,18 @@ RSpec.describe Backup::Repository do
             end
           end
         end
+
+        it 'avoids N+1 database queries' do
+          control_count = ActiveRecord::QueryRecorder.new do
+            subject.dump(max_concurrency: 1, max_storage_concurrency: max_storage_concurrency)
+          end.count
+
+          create_list(:project, 2, :wiki_repo)
+
+          expect do
+            subject.dump(max_concurrency: 1, max_storage_concurrency: max_storage_concurrency)
+          end.not_to exceed_query_limit(control_count)
+        end
       end
     end
   end