[Intel-gfx] [PATCH] drm/i915: Double check vma placement upon gaining the vm lock

[Tvrtko Ursulin]

On 26/11/2019 17:25, Chris Wilson wrote:
> Quoting Chris Wilson (2019-11-26 17:22:23)
>> Quoting Tvrtko Ursulin (2019-11-26 17:04:43)
>>>
>>> On 26/11/2019 15:26, Chris Wilson wrote:
>>>> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
>>>> index e5512f26e20a..f6e661428b02 100644
>>>> --- a/drivers/gpu/drm/i915/i915_vma.c
>>>> +++ b/drivers/gpu/drm/i915/i915_vma.c
>>>> @@ -905,6 +905,12 @@ int i915_vma_pin(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
>>>>                        __i915_vma_set_map_and_fenceable(vma);
>>>>        }
>>>>    
>>>> +     /* Somebody else managed to gazump our placement? */
>>>> +     if (i915_vma_misplaced(vma, size, alignment, flags)) {
>>>> +             err = -EAGAIN;
>>>> +             goto err_active;
>>>> +     }
>>>> +
>>>
>>> What about other callers? They will not be expecting this.
>>
>> The other paths should be quite happy with -EAGAIN from vma_pin, it's
>> already part of their retry procedure. If not, there's always more duct
>> tape. Hopefully the replacement is much simpler (stop laughing back
>> there).
> 
> The alternative here is to pull in __i915_vma_unbind(), which might be
> plausible.

To make unbind and pin atomic? You'd need unlocked vma_pin as well. Or 
some different idea?

Regards,

Tvrtko