From d0d8078013749bb84dc611dfdf6b317512c8559e Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Jonas=20=C3=85dahl?= <jadahl@gmail.com>

Date: Tue, 31 Jul 2018 11:18:51 +0000

Subject: [PATCH] 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 92c61c037..60f36741a 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

-- 

2.19.0