Allow admins to assign locked runners:

app/controllers/admin/runner_projects_controller.rb

@@ -4,8 +4,6 @@ class Admin::RunnerProjectsController < Admin::ApplicationController
   def create
     @runner = Ci::Runner.find(params[:runner_project][:runner_id])
 
-    return head(403) if @runner.locked?
-
     runner_project = @runner.assign_to(@project, current_user)
 
     if runner_project.persisted?

app/views/admin/runners/_runner.html.haml

@@ -4,6 +4,8 @@
       %span.label.label-success shared
     - else
       %span.label.label-info specific
+    - if runner.locked?
+      %span.label.label-danger locked
     - unless runner.active?
       %span.label.label-danger paused
 

app/views/admin/runners/index.html.haml

@@ -40,6 +40,9 @@
           %span.label.label-info specific
           \- run builds from assigned projects
         %li
+          %span.label.label-danger locked
+          \- runner cannot be assigned to other projects
+        %li
           %span.label.label-danger paused
           \- runner will not receive any new builds
 

app/views/admin/runners/show.html.haml

@@ -64,6 +64,9 @@
             = project.name_with_namespace
           %td
             .pull-right
+              - if @runner.locked?
+                = icon('lock', class: 'has-tooltip', title: 'Locked to current projects')
+
               = form_for [:admin, project.namespace.becomes(Namespace), project, project.runner_projects.new] do |f|
                 = f.hidden_field :runner_id, value: @runner.id
                 = f.submit 'Enable', class: 'btn btn-xs'