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

[Jonas Ådahl <jadahl src gnome org>]

commit da9ae90b4c10cbf960e0cfccf74e8c6402bf3910
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    apply out-of-date updates which may contain freed memory.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 0750278ae5..e1ff91568e 100644
--- a/src/backends/native/meta-kms.c
+++ b/src/backends/native/meta-kms.c
@@ -181,6 +181,12 @@ 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 9eae80e3fa..e39f0bfb8f 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 42141460ef..4c6fa5b709 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -1365,6 +1365,7 @@ 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);