[Intel-gfx] [PATCH] drm/i915: Unwind partial VMA rebinding after failure in set-cache-level

[Tvrtko Ursulin]

On 09/10/15 13:19, Chris Wilson wrote:
> On Fri, Oct 09, 2015 at 01:11:47PM +0100, Tvrtko Ursulin wrote:
>>
>> On 09/10/15 12:51, Chris Wilson wrote:
>>> If the impossible happens and we fail to rebind a VMA in the middle of
>>> rebinding all VMA for an object we currently bail out and leave the
>>> object in an inconsistent state. Attempt to unwind the incomplete update
>>> by reverting all updated VMA back to the original cache-level, and WARN
>>> if that fails.
>>
>> Hey a BUG_ON would have been more your style! ;)
>
> Propagating error returns trumps throwing a tantrum and then as we are
> on the the error path we've already proved the impossible could happen,
> so presume it could happen again.

No no, just a BUG_ON(i915_bind_vma()) on the original call site would 
suffice since it cannot happen anyway. ;>

For the same reason it is safe to skip the current entry when reversing 
I suppose.

But it is still code to handle something which can't happen. If you want 
to stuff it under future proofing you can have my r-b, but hope someone 
who doesn't like future proofing notices. :)

Regards,

Tvrtko