[mutter] onscreen/native: Add ref to dumb buffer when using as scanout buffer

[Marge Bot <marge-bot src gnome org>]

commit 36352f44f9547ea1d1564f8b0723d5592d29638a
Author: Jonas Ådahl <jadahl gmail com>
Date:   Wed Feb 24 09:36:52 2021 +0100

    onscreen/native: Add ref to dumb buffer when using as scanout buffer
    
    Each next and current scanout buffer has a reference on them making sure
    they stay alive. When dumb buffers were used on the secondary GPU state,
    this didn't happen, leading to crashes due to unref:ing one time too
    many, with backtraces such as
    
      0) g_type_check_instance_is_fundamentally_a ()
      1) g_object_unref ()
      2) secondary_gpu_release_dumb ()
      3) import_shared_framebuffer ()
      4) update_secondary_gpu_state_post_swap_buffers ()
      5) meta_onscreen_native_swap_buffers_with_damage ()
      6) cogl_onscreen_swap_buffers_with_damage ()
      7) swap_framebuffer ()
      8) clutter_stage_cogl_redraw_view_primary ()
      9) clutter_stage_cogl_redraw_view ()
     10) _clutter_stage_window_redraw_view ()
     11) handle_frame_clock_frame ()
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1746>

 src/backends/native/meta-onscreen-native.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 24b8e5ad7b..b0230d453b 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -782,8 +782,7 @@ copy_shared_framebuffer_primary_gpu (CoglOnscreen                        *onscre
 
   g_object_unref (dmabuf_fb);
 
-  g_clear_object (&secondary_gpu_state->gbm.next_fb);
-  secondary_gpu_state->gbm.next_fb = buffer;
+  g_set_object (&secondary_gpu_state->gbm.next_fb, buffer);
   secondary_gpu_state->cpu.current_dumb_fb = buffer_dumb;
 
   return TRUE;