From b0ee22609a89572d6e3f98eebccf9fb2335dd939 Mon Sep 17 00:00:00 2001
From: Michael Kozono <mkozono@gmail.com>
Date: Fri, 5 May 2017 14:31:33 -0700
Subject: [PATCH] Reduce risk of deadlocks
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We’ve seen a deadlock in CI here https://gitlab.com/mkozono/gitlab-ce/builds/15644492#down-build-trace. This commit should not fix that particular failure, but perhaps it will avoid others.

* Don’t call delete_conflicting_redirects after update if the path wasn’t changed
* Rename descendants without using recursion again, so we can run delete_conflicting_redirects exactly once.
---
 app/models/route.rb       | 24 +++++++++++++++++-------
 spec/models/route_spec.rb | 15 +--------------
 2 files changed, 18 insertions(+), 21 deletions(-)

diff --git a/app/models/route.rb b/app/models/route.rb
index b34cce9077a..12a7fa3d01b 100644
--- a/app/models/route.rb
+++ b/app/models/route.rb
@@ -8,19 +8,19 @@ class Route < ActiveRecord::Base
     presence: true,
     uniqueness: { case_sensitive: false }
 
-  after_save :delete_conflicting_redirects
+  after_create :delete_conflicting_redirects
+  after_update :delete_conflicting_redirects, if: :path_changed?
   after_update :create_redirect_for_old_path
-  after_update :rename_direct_descendant_routes
+  after_update :rename_descendants
 
   scope :inside_path, -> (path) { where('routes.path LIKE ?', "#{sanitize_sql_like(path)}/%") }
-  scope :direct_descendant_routes, -> (path) { where('routes.path LIKE ? AND routes.path NOT LIKE ?', "#{sanitize_sql_like(path)}/%", "#{sanitize_sql_like(path)}/%/%") }
 
-  def rename_direct_descendant_routes
+  def rename_descendants
     return unless path_changed? || name_changed?
 
-    direct_descendant_routes = self.class.direct_descendant_routes(path_was)
+    descendant_routes = self.class.inside_path(path_was)
 
-    direct_descendant_routes.each do |route|
+    descendant_routes.each do |route|
       attributes = {}
 
       if path_changed? && route.path.present?
@@ -31,7 +31,17 @@ class Route < ActiveRecord::Base
         attributes[:name] = route.name.sub(name_was, name)
       end
 
-      route.update(attributes) unless attributes.empty?
+      if attributes.present?
+        old_path = route.path
+
+        # Callbacks must be run manually
+        route.update_columns(attributes)
+
+        # We are not calling route.delete_conflicting_redirects here, in hopes
+        # of avoiding deadlocks. The parent (self, in this method) already
+        # called it, which deletes conflicts for all descendants.
+        route.create_redirect(old_path) if attributes[:path]
+      end
     end
   end
 
diff --git a/spec/models/route_spec.rb b/spec/models/route_spec.rb
index 1aeddcef982..c1fe1b06c52 100644
--- a/spec/models/route_spec.rb
+++ b/spec/models/route_spec.rb
@@ -50,20 +50,7 @@ describe Route, models: true do
     end
   end
 
-  describe '.direct_descendant_routes' do
-    let!(:nested_group) { create(:group, path: 'test', name: 'test', parent: group) }
-    let!(:deep_nested_group) { create(:group, path: 'foo', name: 'foo', parent: nested_group) }
-    let!(:another_group) { create(:group, path: 'other') }
-    let!(:similar_group) { create(:group, path: 'gitllab') }
-    let!(:another_group_nested) { create(:group, path: 'another', name: 'another', parent: similar_group) }
-
-    it 'returns correct routes' do
-      expect(Route.direct_descendant_routes('git_lab')).to match_array([nested_group.route])
-      expect(Route.direct_descendant_routes('git_lab/test')).to match_array([deep_nested_group.route])
-    end
-  end
-
-  describe '#rename_direct_descendant_routes' do
+  describe '#rename_descendants' do
     let!(:nested_group) { create(:group, path: 'test', name: 'test', parent: group) }
     let!(:deep_nested_group) { create(:group, path: 'foo', name: 'foo', parent: nested_group) }
     let!(:similar_group) { create(:group, path: 'gitlab-org', name: 'gitlab-org') }