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

[Frank Binns]

On 28/05/14 08:14, Chris Wilson wrote:
> 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);
>       }
>   }
>   

Hi Chris,
Doesn't this result in the vblank structure never being cleaned up
because the vblank event, which would normally result in it being
destroyed, gets ignored due to present_abort_vblank() being called
a couple of lines above?

I actually submitted a similar patch to this a month ago but never
got around to addressing Keith's review comments. See patch 2
from the following series:
http://lists.x.org/archives/xorg-devel/2014-April/042129.html

I've now gone back to looking at this so that I can address the
comments and resubmit the patches.

Thanks
Frank