linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915: fix infinite recursion on unbind due to ilk vt-d w/a

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Date:	Tue, 6 Dec 2011 09:43:17 -0800
From:	Ben Widawsky <ben@...dawsk.net>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
Cc:	Dave Airlie <airlied@...il.com>, intel-gfx@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915: fix infinite recursion on unbind
 due to ilk vt-d w/a

On Tue, Dec 06, 2011 at 12:12:33PM +0100, Daniel Vetter wrote:
> The recursion loop goes retire_requests->unbind->gpu_idle->retire_reqeusts.
> 
> Every time we go through this we need a
> - active object that can be retired
> - and there are no other references to that object than the one from
>   the active list, so that it gets unbound and freed immediately.
> Otherwise the recursion stops. So the recursion is only limited by the
> number of objects that fit these requirements sitting in the active list
> any time retire_request is called.
> 
> Issue exercised by tests/gem_unref_active_buffers from i-g-t.
> 
> There's been a decent bikeshed discussion whether it wouldn't be
> better to pass around a flag, but imo this is o.k. for such a limited
> case that only supports a w/a.
> 
> Signed-Off-by: Daniel Vetter <daniel.vetter@...ll.ch>
> Reviewed-by: Chris Wilson <chris@...is-wilson> # we built better
> 	bikesheds, but this keeps the rain off for now
> ---

What about:
http://lists.freedesktop.org/archives/intel-gfx/2011-October/012984.html


Did someone prove that doesn't work?
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