[mutter/cherry-pick-8e91c629-2] renderer/native: Clear old KMS updates on views rebuild

[Jonas Ådahl <jadahl src gnome org>]

commit 84009175fb2ca71aa7db1dbae3856a492183b592
Author: Jonas Ådahl <jadahl gmail com>
Date:   Fri Jan 7 22:27:51 2022 +0100

    renderer/native: Clear old KMS updates on views rebuild
    
    If there are any pending updates, for example if we painted one of
    multiple monitors but without having posted the update due to waiting
    for another monitor to be painted, but before we paint all of them and
    post the update, another hotplug event happens, we'd have stale pending
    KMS update. When that update eventually would be processed, we'd try to
    apply out-of-date updates which may contain freed memory.
    
    Fix this by discarding any update when we're rebuilding the views. We
    can be sure not to need any of the old updates since we're rebuilding
    the whole content anyway.
    
    Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1928
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2216>
    
    
    (cherry picked from commit 8e91c6295dd38cf5b4d60e8069eb955218a94edb)

 src/backends/native/meta-kms.c             | 6 ++++++
 src/backends/native/meta-kms.h             | 2 ++
 src/backends/native/meta-renderer-native.c | 1 +
 3 files changed, 9 insertions(+)
---
diff --git a/src/backends/native/meta-kms.c b/src/backends/native/meta-kms.c
index edb6f29eec..13ee90f526 100644
--- a/src/backends/native/meta-kms.c
+++ b/src/backends/native/meta-kms.c
@@ -179,6 +179,12 @@ struct _MetaKms
 
 G_DEFINE_TYPE (MetaKms, meta_kms, G_TYPE_OBJECT)
 
+void
+meta_kms_discard_pending_updates (MetaKms *kms)
+{
+  g_clear_list (&kms->pending_updates, (GDestroyNotify) meta_kms_update_free);
+}
+
 static void
 meta_kms_add_pending_update (MetaKms       *kms,
                              MetaKmsUpdate *update)
diff --git a/src/backends/native/meta-kms.h b/src/backends/native/meta-kms.h
index 79713cc405..6f55bb445f 100644
--- a/src/backends/native/meta-kms.h
+++ b/src/backends/native/meta-kms.h
@@ -40,6 +40,8 @@ typedef enum _MetaKmsUpdateFlag
 #define META_TYPE_KMS (meta_kms_get_type ())
 G_DECLARE_FINAL_TYPE (MetaKms, meta_kms, META, KMS, GObject)
 
+void meta_kms_discard_pending_updates (MetaKms *kms);
+
 MetaKmsUpdate * meta_kms_ensure_pending_update (MetaKms       *kms,
                                                 MetaKmsDevice *device);
 
diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index 7e4af8fe0c..735c37202d 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -1174,6 +1174,7 @@ meta_renderer_native_rebuild_views (MetaRenderer *renderer)
     META_RENDERER_CLASS (meta_renderer_native_parent_class);
 
   meta_kms_discard_pending_page_flips (kms);
+  meta_kms_discard_pending_updates (kms);
 
   keep_current_onscreens_alive (renderer);