platforms/drm: check wl_eglstream buffers before attaching

If a wl_eglstream buffer is attached to a surface, but then later a different
type of buffer, such as a dmabuf, is attached to the same surface, kwin will
mistakenly keep trying to acquire frames from the EGLStream associated with the
previous buffer. This can happen if an Xwayland window is made full-screen
causing it to switch to the flipping presentation path, for instance. The
result is that the window contents will no longer be updated.

Instead, the eglstream backend's loadTexture and updateTexture functions should
first pass the buffer to eglCreateStreamAttribNV. If it fails with
EGL_BAD_STREAM_KHR, that indicates it is indeed a wl_eglstream, and that we've
already associated a server-side EGLStream with it in attachStreamConsumer, so
we can proceed as usual. If it fails with EGL_BAD_ACCESS, though, that
indicates it is not a wl_eglstream and we should fall back to the parent class
which handles attaching other buffer types. If it doesn't fail at all, that
means the client tried to attach a new wl_eglstream to a surface without first
attaching the stream consumer. There's not really a great way to handle this,
so just re-use the previous EGLStream.

src/plugins/platforms/drm/egl_stream_backend.cpp

@@ -197,6 +197,13 @@ EglStreamBackend::StreamTexture *EglStreamBackend::lookupStreamTexture(KWaylandS
            nullptr;
 }
 
+void EglStreamBackend::destroyStreamTexture(KWaylandServer::SurfaceInterface *surface)
+{
+    const StreamTexture &st = m_streamTextures.take(surface);
+    pEglDestroyStreamKHR(eglDisplay(), st.stream);
+    glDeleteTextures(1, &st.texture);
+}
+
 void EglStreamBackend::attachStreamConsumer(KWaylandServer::SurfaceInterface *surface,
                                             void *eglStream,
                                             wl_array *attribs)
@@ -231,9 +238,7 @@ void EglStreamBackend::attachStreamConsumer(KWaylandServer::SurfaceInterface *su
         connect(surface, &KWaylandServer::SurfaceInterface::destroyed, this,
             [surface, this]() {
                 makeCurrent();
-                const StreamTexture &st = m_streamTextures.take(surface);
-                pEglDestroyStreamKHR(eglDisplay(), st.stream);
-                glDeleteTextures(1, &st.texture);
+                destroyStreamTexture(surface);
             });
     }
 
@@ -654,12 +659,43 @@ bool EglStreamSurfaceTextureWayland::attachBuffer(KWaylandServer::BufferInterfac
     return oldFormat != m_format || wasYInverted != texture()->isYInverted();
 }
 
+bool EglStreamSurfaceTextureWayland::checkBuffer(KWaylandServer::SurfaceInterface *surface,
+                                                 KWaylandServer::BufferInterface *buffer)
+{
+    EGLAttrib attribs[] = {
+        EGL_WAYLAND_EGLSTREAM_WL, (EGLAttrib)buffer->resource(),
+        EGL_NONE
+    };
+    EGLStreamKHR stream = pEglCreateStreamAttribNV(m_backend->eglDisplay(), attribs);
+    if (stream == EGL_NO_STREAM_KHR) {
+        // eglCreateStreamAttribNV generates EGL_BAD_ACCESS if the
+        // provided buffer is not a wl_eglstream. In that case, clean up
+        // the old stream and fall back to the dmabuf or shm attach
+        // paths.
+        EGLint err = eglGetError();
+        if (err == EGL_BAD_ACCESS) {
+            m_backend->destroyStreamTexture(surface);
+            return false;
+        }
+        // Otherwise it should have generated EGL_BAD_STREAM_KHR since
+        // we've already created an EGLStream for it.
+        Q_ASSERT(err == EGL_BAD_STREAM_KHR);
+    } else {
+        // If eglCreateStreamAttribNV *didn't* fail, that means the
+        // buffer is a wl_eglstream but it hasn't been attached to a
+        // consumer for some reason. Not much we can do here.
+        qCCritical(KWIN_DRM) << "Untracked wl_eglstream attached to surface";
+        pEglDestroyStreamKHR(m_backend->eglDisplay(), stream);
+    }
+    return true;
+}
+
 bool EglStreamSurfaceTextureWayland::create()
 {
     using namespace KWaylandServer;
     SurfaceInterface *surface = m_pixmap->surface();
     const EglStreamBackend::StreamTexture *st = m_backend->lookupStreamTexture(surface);
-    if (m_pixmap->buffer() && st != nullptr) {
+    if (m_pixmap->buffer() && st != nullptr && checkBuffer(surface, m_pixmap->buffer())) {
 
         glGenTextures(1, &m_textureId);
         m_texture.reset(new GLTexture(m_textureId, 0, m_pixmap->buffer()->size()));
@@ -687,7 +723,7 @@ void EglStreamSurfaceTextureWayland::update(const QRegion &region)
     using namespace KWaylandServer;
     SurfaceInterface *surface = m_pixmap->surface();
     const EglStreamBackend::StreamTexture *st = m_backend->lookupStreamTexture(surface);
-    if (m_pixmap->buffer() && st != nullptr) {
+    if (m_pixmap->buffer() && st != nullptr && checkBuffer(surface, m_pixmap->buffer())) {
 
         if (attachBuffer(surface->buffer())) {
             createFbo();

src/plugins/platforms/drm/egl_stream_backend.h

@@ -57,6 +57,7 @@ private:
         GLuint texture;
     };
     StreamTexture *lookupStreamTexture(KWaylandServer::SurfaceInterface *surface);
+    void destroyStreamTexture(KWaylandServer::SurfaceInterface *surface);
     void attachStreamConsumer(KWaylandServer::SurfaceInterface *surface,
                               void *eglStream,
                               wl_array *attribs);
@@ -96,6 +97,8 @@ private:
     void createFbo();
     void copyExternalTexture(GLuint tex);
     bool attachBuffer(KWaylandServer::BufferInterface *buffer);
+    bool checkBuffer(KWaylandServer::SurfaceInterface *surface,
+                     KWaylandServer::BufferInterface *buffer);
 
     EglStreamBackend *m_backend;
     GLuint m_fbo, m_rbo, m_textureId;