[Intel-gfx] [PATCH] drm/i915: Ensure associated VMAs are inactive when contexts are destroyed

[Chris Wilson]

On Mon, Oct 26, 2015 at 11:05:03AM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> In the following commit:
> 
>     commit e9f24d5fb7cf3628b195b18ff3ac4e37937ceeae
>     Author: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>     Date:   Mon Oct 5 13:26:36 2015 +0100
> 
>         drm/i915: Clean up associated VMAs on context destruction
> 
> I added a WARN_ON assertion that VM's active list must be empty
> at the time of owning context is getting freed, but that turned
> out to be a wrong assumption.
> 
> Due ordering of operations in i915_gem_object_retire__read, where
> contexts are unreferenced before VMAs are moved to the inactive
> list, the described situation can in fact happen.

The context is being unreferenced indirectly. Adding a direct reference
here is even more bizarre.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre