[PATCH 5/6] present: Do not free screen_priv->flip_pending until it is finished

[Chris Wilson]

If we close the Window prior to completing all the flips, we free the
vblank pointer but leave screen_priv->flip_pending dangling. This leads
to a host of invalid reads/writes as it is accessed from many locations,
e.g.:

==20302== Invalid write of size 4
==20302==    at 0x81A8FD5: present_flip_destroy (present.c:879)
==20302==    by 0x81A6A2A: present_close_screen (present_screen.c:60)
==20302==    by 0x8147A5A: CursorCloseScreen (cursor.c:187)
==20302==    by 0x81A3DDA: AnimCurCloseScreen (animcur.c:106)
==20302==    by 0x8142F7D: compCloseScreen (compinit.c:85)
==20302==    by 0x80E6D2A: VidModeClose (xf86VidMode.c:111)
==20302==    by 0x496CF23: glxCloseScreen (glxscreens.c:187)
==20302==    by 0x808186F: dix_main (main.c:349)
==20302==    by 0x80D2FA1: main (stubmain.c:34)
==20302==  Address 0x67d0780 is 104 bytes inside a block of size 108 free'd
==20302==    at 0x4007BCD: free (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==20302==    by 0x81A90AC: present_vblank_destroy (present.c:911)
==20302==    by 0x81A6ADF: present_free_window_vblank (present_screen.c:79)
==20302==    by 0x81A6C2C: present_destroy_window (present_screen.c:116)
==20302==    by 0x8145796: compDestroyWindow (compwindow.c:608)
==20302==    by 0x8176B6B: DbeDestroyWindow (dbe.c:1318)
==20302==    by 0x80B5A98: FreeWindowResources (window.c:910)
==20302==    by 0x80B5D7B: DeleteWindow (window.c:978)
==20302==    by 0x80A9C85: doFreeResource (resource.c:873)
==20302==    by 0x80AA5F8: FreeClientResources (resource.c:1139)
==20302==    by 0x807BD5E: CloseDownClient (dispatch.c:3384)
==20302==    by 0x80740B5: Dispatch (dispatch.c:406)

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 present/present_screen.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/present/present_screen.c b/present/present_screen.c
index b475d03..0a525a8 100644
--- a/present/present_screen.c
+++ b/present/present_screen.c
@@ -72,11 +72,14 @@ static void
 present_free_window_vblank(WindowPtr window)
 {
     present_window_priv_ptr     window_priv = present_window_priv(window);
+    present_screen_priv_ptr     screen_priv = present_screen_priv(window->drawable.pScreen);
+    present_vblank_ptr          flip_pending = screen_priv->flip_pending;
     present_vblank_ptr          vblank, tmp;
 
     xorg_list_for_each_entry_safe(vblank, tmp, &window_priv->vblank, window_list) {
         present_abort_vblank(window->drawable.pScreen, vblank->crtc, vblank->event_id, vblank->target_msc);
-        present_vblank_destroy(vblank);
+        if (vblank != flip_pending)
+            present_vblank_destroy(vblank);
     }
 }
 
-- 
2.0.0.rc2