cursor-renderer/native: Create all view objects before realizing

Realizing a cursor will assume view related state objects are valid so
they can mark them as dirty. This assumption broke when there were a
scale changed that happened with multiple CRTCs, as we'd create view
object by view object as we realized the texture. Realizing the texture
would trigger a signal that had the handler assuming the validity of all
view objects, but if we only had gotten to the first, the second view
would not be there yet, thus we'd be doing a NULL pointer dereference.

Creating the view objects first, then handling the updating avoids this
problem by making the already done assumption valid on hotplugs.

The test case added tests exactly this series of events, and uses a
virtual monitor as a cheap trick to make the KMS CRTC based view the
first one, and an arbitrary view the second that previously had its view
object initialized too late.

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/3012
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3262>

src/backends/native/meta-crtc-virtual.h

@@ -20,6 +20,7 @@
 #include "backends/native/meta-crtc-native.h"
 
 #define META_TYPE_CRTC_VIRTUAL (meta_crtc_virtual_get_type ())
+META_EXPORT_TEST
 G_DECLARE_FINAL_TYPE (MetaCrtcVirtual, meta_crtc_virtual,
                       META, CRTC_VIRTUAL,
                       MetaCrtcNative)

src/backends/native/meta-cursor-renderer-native.c

@@ -315,6 +315,8 @@ meta_cursor_renderer_native_update_cursor (MetaCursorRenderer *cursor_renderer,
   cursor_changed = priv->current_cursor != cursor_sprite;
 
   views = meta_renderer_get_views (renderer);
+  g_list_foreach (views, (GFunc) ensure_cursor_stage_view, NULL);
+
   for (l = views; l; l = l->next)
     {
       MetaStageView *view = l->data;
@@ -324,7 +326,8 @@ meta_cursor_renderer_native_update_cursor (MetaCursorRenderer *cursor_renderer,
       CursorStageView *cursor_stage_view = NULL;
       gboolean has_hw_cursor = FALSE;
 
-      cursor_stage_view = ensure_cursor_stage_view (view);
+      cursor_stage_view = get_cursor_stage_view (view);
+      g_assert (cursor_stage_view);
 
       if (!META_IS_CRTC_KMS (crtc) ||
           !meta_crtc_native_is_hw_cursor_supported (crtc_native))

src/tests/monitor-configs/kms-cursor-scale.xml

@@ -0,0 +1,41 @@
+<monitors version="2">
+  <configuration>
+    <logicalmonitor>
+      <x>0</x>
+      <y>0</y>
+      <scale>2</scale>
+      <primary>yes</primary>
+      <monitor>
+	<monitorspec>
+	  <connector>Virtual-1</connector>
+	  <vendor>unknown</vendor>
+	  <product>unknown</product>
+	  <serial>unknown</serial>
+	</monitorspec>
+	<mode>
+	  <width>1024</width>
+	  <height>768</height>
+	  <rate>60.003841</rate>
+	</mode>
+      </monitor>
+    </logicalmonitor>
+    <logicalmonitor>
+      <x>512</x>
+      <y>0</y>
+      <primary>no</primary>
+      <monitor>
+	<monitorspec>
+	  <connector>Meta-0</connector>
+	  <vendor>MetaTestVendor</vendor>
+	  <product>MetaVirtualMonitor</product>
+	  <serial>0x1234</serial>
+	</monitorspec>
+	<mode>
+	  <width>100</width>
+	  <height>100</height>
+	  <rate>60</rate>
+	</mode>
+      </monitor>
+    </logicalmonitor>
+  </configuration>
+</monitors>

src/tests/native-kms-cursor-hotplug.c

@@ -20,6 +20,10 @@
 
 #include "backends/meta-monitor-config-manager.h"
 #include "backends/meta-virtual-monitor.h"
+#include "backends/native/meta-backend-native.h"
+#include "backends/native/meta-crtc-kms.h"
+#include "backends/native/meta-crtc-virtual.h"
+#include "backends/native/meta-udev.h"
 #include "core/window-private.h"
 #include "meta-test/meta-context-test.h"
 #include "meta/meta-backend.h"
@@ -35,6 +39,12 @@
 
 static MetaContext *test_context;
 
+static void
+set_true_cb (gboolean *done)
+{
+  *done = TRUE;
+}
+
 static void
 meta_test_cursor_hotplug (void)
 {
@@ -139,11 +149,74 @@ meta_test_cursor_hotplug (void)
   meta_wait_for_paint (test_context);
 }
 
+static void
+meta_test_hotplug_multi_view_invalidation (void)
+{
+  MetaBackend *backend = meta_context_get_backend (test_context);
+  MetaMonitorManager *monitor_manager =
+    meta_backend_get_monitor_manager (backend);
+  MetaRenderer *renderer = meta_backend_get_renderer (backend);
+  MetaCursorRenderer *cursor_renderer = meta_backend_get_cursor_renderer (backend);
+  ClutterSeat *seat;
+  g_autoptr (MetaVirtualMonitorInfo) monitor_info = NULL;
+  MetaVirtualMonitor *virtual_monitor;
+  g_autoptr (ClutterVirtualInputDevice) virtual_pointer = NULL;
+  MetaCursorSprite *cursor_sprite;
+  gboolean texture_changed;
+  gulong texture_changed_handler_id;
+  g_autoptr (GError) error = NULL;
+  GList *views;
+
+  seat = meta_backend_get_default_seat (backend);
+  virtual_pointer = clutter_seat_create_virtual_device (seat,
+                                                        CLUTTER_POINTER_DEVICE);
+
+  monitor_info = meta_virtual_monitor_info_new (100, 100, 60.0,
+                                                "MetaTestVendor",
+                                                "MetaVirtualMonitor",
+                                                "0x1234");
+  virtual_monitor = meta_monitor_manager_create_virtual_monitor (monitor_manager,
+                                                                 monitor_info,
+                                                                 &error);
+  g_assert_no_error (error);
+
+  meta_monitor_manager_reload (monitor_manager);
+  views = meta_renderer_get_views (renderer);
+  g_assert_true (META_IS_CRTC_KMS (meta_renderer_view_get_crtc (views->data)));
+  g_assert_true (META_IS_CRTC_VIRTUAL (meta_renderer_view_get_crtc (views->next->data)));
+
+  meta_wait_for_paint (test_context);
+
+  cursor_sprite = meta_cursor_renderer_get_cursor (cursor_renderer);
+  g_assert_nonnull (cursor_sprite);
+  texture_changed_handler_id =
+    g_signal_connect_swapped (cursor_sprite, "texture-changed",
+                              G_CALLBACK (set_true_cb), &texture_changed);
+
+  /* Trigger a cursor scale change, that causes invalidation on a non-first
+   * KMS CRTC based cursor renderer view auxiliary object.
+   */
+  texture_changed = FALSE;
+  meta_set_custom_monitor_config_full (backend, "kms-cursor-scale.xml",
+                                       META_MONITORS_CONFIG_FLAG_NONE);
+  meta_monitor_manager_reload (monitor_manager);
+  views = meta_renderer_get_views (renderer);
+  g_assert_true (META_IS_CRTC_KMS (meta_renderer_view_get_crtc (views->data)));
+  g_assert_true (META_IS_CRTC_VIRTUAL (meta_renderer_view_get_crtc (views->next->data)));
+  g_assert_true (texture_changed);
+
+  g_signal_handler_disconnect (cursor_sprite, texture_changed_handler_id);
+  g_clear_object (&virtual_monitor);
+  meta_wait_for_paint (test_context);
+}
+
 static void
 init_tests (void)
 {
   g_test_add_func ("/wayland/cursor-hotplug",
                    meta_test_cursor_hotplug);
+  g_test_add_func ("/hotplug/multi-view-invalidation",
+                   meta_test_hotplug_multi_view_invalidation);
 }
 
 int