[mutter/wip/texture-purge-on-nvidia: 22/66] monitor: Use current monitor mode to check whether active

[Ray Strode <halfline src gnome org>]

commit 30c614e8546d039587cf344aebb92f1bfb177e06
Author: Jonas Ådahl <jadahl gmail com>
Date:   Tue Jul 31 11:18:51 2018 +0000

    monitor: Use current monitor mode to check whether active
    
    For historical reasons meta_monitor_is_active() checked whether it is
    active by checking whether the main output have a CRTC assigned and
    whether that CRTC has a current mode. At a later point, the MetaMonitor
    got its own mode abstraction (MetaMonitorMode), but
    meta_monitor_is_active() was never updated to use this.
    
    An issue with checking the main output's CRTC state is that, if there is
    some CRTC mode combination that for some reason isn't properly detected
    by the MetaMonitorMode abstraction (e.g. some tiling configuration not
    yet handled), meta_monitor_is_active() would return TRUE, even though no
    (abstracted) mode was set. This would cause confusion here and there,
    leading to NULL pointer dereferences due to the assumption that if a
    monitor is active, it has an active mode.
    
    Instead, change meta_monitor_is_active() to directly check the current
    monitor mode, and log a warning if the main output still happen to have
    a CRTC with a mode assigned to it. This way, when an not undrestood CRTC
    mode combination is encountered, instead of dereferencing NULL pointers,
    simply assume the monitor is not active, which means that it will not be
    managed or rendered by mutter at all.
    
    https://gitlab.gnome.org/GNOME/mutter/issues/130
    
    (cherry picked from commit 4d465eac0806eb1ead375e2852d4a9d6bc24524f)

 src/backends/meta-monitor.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)
---
diff --git a/src/backends/meta-monitor.c b/src/backends/meta-monitor.c
index 98330661e..9a412a612 100644
--- a/src/backends/meta-monitor.c
+++ b/src/backends/meta-monitor.c
@@ -203,13 +203,9 @@ meta_monitor_get_main_output (MetaMonitor *monitor)
 gboolean
 meta_monitor_is_active (MetaMonitor *monitor)
 {
-  MetaOutput *output;
-  MetaCrtc *crtc;
-
-  output = meta_monitor_get_main_output (monitor);
-  crtc = meta_output_get_assigned_crtc (output);
+  MetaMonitorPrivate *priv = meta_monitor_get_instance_private (monitor);
 
-  return crtc && crtc->current_mode;
+  return !!priv->current_mode;
 }
 
 gboolean
@@ -1411,6 +1407,18 @@ meta_monitor_get_current_mode (MetaMonitor *monitor)
   return priv->current_mode;
 }
 
+static gboolean
+is_current_mode_known (MetaMonitor *monitor)
+{
+  MetaOutput *output;
+  MetaCrtc *crtc;
+
+  output = meta_monitor_get_main_output (monitor);
+  crtc = meta_output_get_assigned_crtc (output);
+
+  return meta_monitor_is_active (monitor) == (crtc && crtc->current_mode);
+}
+
 void
 meta_monitor_derive_current_mode (MetaMonitor *monitor)
 {
@@ -1430,6 +1438,8 @@ meta_monitor_derive_current_mode (MetaMonitor *monitor)
     }
 
   priv->current_mode = current_mode;
+
+  g_warn_if_fail (is_current_mode_known (monitor));
 }
 
 void