loader/dri3: Use dri3_find_back in loader_dri3_swap_buffers_msc

If the application hasn't done any drawing since the last call, we
would reuse the same back buffer which was used for the previous swap,
which may not have completed yet. This could result in various issues
such as tearing or application hangs.

In the normal case, the behaviour is unchanged.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97957
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101683
Cc: mesa-stable@lists.freedesktop.org
[Michel Dänzer: Make Thomas' fix from bugzilla actually work as
 intended, write commit log]

diff --git a/src/loader/loader_dri3_helper.c b/src/loader/loader_dri3_helper.c
index 493a7f5..1c93e7a 100644 (file)
--- a/src/loader/loader_dri3_helper.c
+++ b/src/loader/loader_dri3_helper.c
@@ -640,7 +640,7 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw,
 
    draw->vtable->flush_drawable(draw, flush_flags);
 
-   back = draw->buffers[LOADER_DRI3_BACK_ID(draw->cur_back)];
+   back = draw->buffers[dri3_find_back(draw)];
    if (draw->is_different_gpu && back) {
       /* Update the linear buffer before presenting the pixmap */
       draw->ext->image->blitImage(dri_context,