From e0a8fa778e3dce508695155c7d5a9a1e0bddd9f8 Mon Sep 17 00:00:00 2001
From: Xaver Hugl <xaver.hugl@gmail.com>
Date: Tue, 18 Jan 2022 21:36:23 +0000
Subject: [PATCH] backends/drm: fix output changes with the placeholder output

As the placeholder output gets added or removed in response to other outputs
getting enabled or disabled, the output list may change while iterating over
them and applying changes.

BUG: 448454
BUG: 448474
CCBUG: 448697
FIXED-IN: 5.24
---
 src/backends/drm/drm_backend.cpp | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/backends/drm/drm_backend.cpp b/src/backends/drm/drm_backend.cpp
index 96d7a4e4b8..a2fd6208d6 100644
--- a/src/backends/drm/drm_backend.cpp
+++ b/src/backends/drm/drm_backend.cpp
@@ -632,10 +632,14 @@ bool DrmBackend::applyOutputChanges(const WaylandOutputConfig &config)
             return false;
         }
     }
+    // first, apply changes to drm outputs.
+    // This may remove the placeholder output and thus change m_outputs!
+    for (const auto &output : qAsConst(changed)) {
+        output->applyQueuedChanges(config);
+    }
+    // only then apply changes to the virtual outputs
     for (const auto &output : qAsConst(m_outputs)) {
-        if (auto drmOutput = qobject_cast<DrmOutput*>(output)) {
-            drmOutput->applyQueuedChanges(config);
-        } else {
+        if (!qobject_cast<DrmOutput*>(output)) {
             output->applyChanges(config);
         }
     };