[PATCH] xwayland: Destroy wl_buffers only after they are released

[Axel Davy]

Hi,

I have pending changes to this part to implement XWayland present support.

Instead a having the wl_buffer attached to a window, I attach it to a 
pixmap.

Could you test with this branch, and tell if you encounter the problems 
you have?

https://github.com/axeldavy/xserver/tree/xwayland-dri3-present

Thanks.

Axel Davy

On 11/02/2014, Rui Matos wrote :
> Destroying a wl_buffer that is still attached to a wl_surface is
> undefined behavior according to the wayland protocol. We should delay
> the destruction until we get the release event.
> ---
>
> So, I'm not sure why there was this comment saying that it was safe to
> do this, perhaps it was in an old protocol version?
>
> In any case, this has been making xwayland crash under mutter ever
> since this mutter commit
> https://git.gnome.org/browse/mutter/commit/?h=wayland&id=3e98ffaf9958366b584b360ac12bbc03cd070c07 .
>
>   hw/xfree86/xwayland/xwayland-window.c | 16 ++++++++++++----
>   1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/hw/xfree86/xwayland/xwayland-window.c b/hw/xfree86/xwayland/xwayland-window.c
> index a2a8206..a005cc6 100644
> --- a/hw/xfree86/xwayland/xwayland-window.c
> +++ b/hw/xfree86/xwayland/xwayland-window.c
> @@ -43,6 +43,16 @@
>   static DevPrivateKeyRec xwl_window_private_key;
>   
>   static void
> +free_buffer(void *data, struct wl_buffer *buffer)
> +{
> +    wl_buffer_destroy(buffer);
> +}
> +
> +static const struct wl_buffer_listener buffer_listener = {
> +    free_buffer,
> +};
> +
> +static void
>   free_pixmap(void *data, struct wl_callback *callback, uint32_t time)
>   {
>       PixmapPtr pixmap = data;
> @@ -62,10 +72,8 @@ xwl_window_attach(struct xwl_window *xwl_window, PixmapPtr pixmap)
>       struct xwl_screen *xwl_screen = xwl_window->xwl_screen;
>       struct wl_callback *callback;
>   
> -    /* We can safely destroy the buffer because we only use one buffer
> -     * per surface in xwayland model */
>       if (xwl_window->buffer)
> -        wl_buffer_destroy(xwl_window->buffer);
> +        wl_buffer_add_listener(xwl_window->buffer, &buffer_listener, NULL);
>   
>       xwl_screen->driver->create_window_buffer(xwl_window, pixmap);
>   
> @@ -185,7 +193,7 @@ xwl_unrealize_window(WindowPtr window)
>   	return ret;
>   
>       if (xwl_window->buffer)
> -	wl_buffer_destroy(xwl_window->buffer);
> +        wl_buffer_add_listener(xwl_window->buffer, &buffer_listener, NULL);
>       wl_surface_destroy(xwl_window->surface);
>       xorg_list_del(&xwl_window->link);
>       if (RegionNotEmpty(DamageRegion(xwl_window->damage)))

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