Don't remove outputs during page flip

Summary:
To do so leaves a dangling pointer on our pageFlipHandler

BUG: 396272

Test Plan: Wobbled a window whilst plugging a monitor in and out

Reviewers: #kwin

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D14210

plugins/platforms/drm/drm_backend.cpp

@@ -400,7 +400,7 @@ void DrmBackend::updateOutputs()
         it = m_outputs.erase(it);
         m_enabledOutputs.removeOne(removed);
         emit outputRemoved(removed);
-        delete removed;
+        removed->teardown();
     }
 
     // now check new connections

plugins/platforms/drm/drm_output.cpp

@@ -65,6 +65,15 @@ DrmOutput::DrmOutput(DrmBackend *backend)
 
 DrmOutput::~DrmOutput()
 {
+    Q_ASSERT(!m_pageFlipPending);
+    if (!m_deleted) {
+        teardown();
+    }
+}
+
+void DrmOutput::teardown()
+{
+    m_deleted = true;
     hideCursor();
     m_crtc->blank();
 
@@ -85,6 +94,10 @@ DrmOutput::~DrmOutput()
     delete m_waylandOutputDevice.data();
     delete m_cursor[0];
     delete m_cursor[1];
+    if (!m_pageFlipPending) {
+        deleteLater();
+    } //else will be deleted in the page flip handler
+    //this is needed so that the pageflipcallback handle isn't deleted
 }
 
 void DrmOutput::releaseGbm()
@@ -947,6 +960,10 @@ void DrmOutput::updateMode(int modeIndex)
 void DrmOutput::pageFlipped()
 {
     m_pageFlipPending = false;
+    if (m_deleted) {
+        deleteLater();
+        return;
+    }
 
     if (!m_crtc) {
         return;

plugins/platforms/drm/drm_output.h

@@ -65,7 +65,10 @@ public:
         QByteArray serialNumber;
         QSize physicalSize;
     };
-    virtual ~DrmOutput();
+    ///deletes the output, calling this whilst a page flip is pending will result in an error
+    ~DrmOutput() override;
+    ///queues deleting the output after a page flip has completed.
+    void teardown();
     void releaseGbm();
     bool showCursor(DrmDumbBuffer *buffer);
     bool showCursor();
@@ -145,6 +148,7 @@ private:
     friend class DrmCrtc;   // TODO: For use of setModeLegacy. Remove later when we allow multiple connectors per crtc
                             //       and save the connector ids in the DrmCrtc instance.
     DrmOutput(DrmBackend *backend);
+
     bool presentAtomically(DrmBuffer *buffer);
 
     enum class AtomicCommitMode {
@@ -214,6 +218,7 @@ private:
     int m_cursorIndex = 0;
     bool m_hasNewCursor = false;
     bool m_internal = false;
+    bool m_deleted = false;
 };
 
 }