[Intel-gfx] [PATCH 26/43] drm/i915: Only clear the GPU domains upon a successful finish

[Daniel Vetter]

On Wed, Dec 14, 2011 at 01:57:23PM +0100, Daniel Vetter wrote:
> From: Chris Wilson <chris at chris-wilson.co.uk>
> 
> By clearing the GPU read domains before waiting upon the buffer, we run
> the risk of the wait being interrupted and the domains prematurely
> cleared. The next time we attempt to wait upon the buffer (after
> userspace handles the signal), we believe that the buffer is idle and so
> skip the wait.
> 
> There are a number of bugs across all generations which show signs of an
> overly haste reuse of active buffers.
> 
> Such as:
> 
>   https://bugs.freedesktop.org/show_bug.cgi?id=29046
>   https://bugs.freedesktop.org/show_bug.cgi?id=35863
>   https://bugs.freedesktop.org/show_bug.cgi?id=38952
>   https://bugs.freedesktop.org/show_bug.cgi?id=40282
>   https://bugs.freedesktop.org/show_bug.cgi?id=41098
>   https://bugs.freedesktop.org/show_bug.cgi?id=41102
>   https://bugs.freedesktop.org/show_bug.cgi?id=41284
>   https://bugs.freedesktop.org/show_bug.cgi?id=42141
> 
> A couple of those pre-date i915_gem_object_finish_gpu(), so may be
> unrelated (such as a wild write from a userspace command buffer), but
> this does look like a convincing cause for most of those bugs.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: stable at kernel.org
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> Reviewed-by: Eugeni Dodonov <eugeni.dodonov at intel.com>

I really hate it that we have neither a solid testcase nor a decen
explanation for how exactly this fixes issues. But there have been too
many reports from people that this patch here at least improves matters.

/me grumpily merges this for -next.

-Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48