eglfs_kms: Prevent drm errors with more than one window during the screen's lifetime

The QML Live Preview tool exercises the problematic case of having a
QQuickWindow, then closing it, then showing another, then destroying
that, ..., and so on.

It seems that the eglfs_kms backend does not handle this gracefully:
if there was a page flip issued for a window that is then closed, the
new window will result in drm errors (like -22 EINVAL) because the
logic gets confused due to holding on to surface buffers from the old
window.

To remedy this, make sure the same cleanup is performed on a failing
atomic commit as it is done on the non-atomic code path. In addition,
reset more things in resetSurface().

Change-Id: I7e13dbbf4d74b4ed9beaf71472680a0daafb4f95
Fixes: QTBUG-82104
Reviewed-by: Christian Strømme <christian.stromme@qt.io>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmscreen.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmscreen.cpp
index 722d0266ce..0f829ee00c 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmscreen.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmscreen.cpp
@@ -161,6 +161,9 @@ gbm_surface *QEglFSKmsGbmScreen::createSurface(EGLConfig eglConfig)
 
 void QEglFSKmsGbmScreen::resetSurface()
 {
+    m_flipPending = false;
+    m_gbm_bo_current = nullptr;
+    m_gbm_bo_next = nullptr;
     m_gbm_surface = nullptr;
 }
 
@@ -423,9 +426,15 @@ void QEglFSKmsGbmScreen::flip()
         }
     }
 
+    if (device()->hasAtomicSupport()) {
 #if QT_CONFIG(drm_atomic)
-    device()->threadLocalAtomicCommit(this);
+        if (!device()->threadLocalAtomicCommit(this)) {
+            m_flipPending = false;
+            gbm_surface_release_buffer(m_gbm_surface, m_gbm_bo_next);
+            m_gbm_bo_next = nullptr;
+        }
 #endif
+    }
 }
 
 void QEglFSKmsGbmScreen::flipFinished()