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

Chris Wilson chris at chris-wilson.co.uk
Mon Oct 26 04:23:07 PDT 2015

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 Wilson, Intel Open Source Technology Centre

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