[PATCH 1/2] dma-buf: make reservation_object_copy_fences rcu save

[Christian König]

Am 11.09.2017 um 17:22 schrieb Christian König:
> Am 11.09.2017 um 17:13 schrieb Maarten Lankhorst:
>> Op 11-09-17 om 16:45 schreef Christian König:
>>> Am 11.09.2017 um 15:56 schrieb Maarten Lankhorst:
>>>> Op 11-09-17 om 14:53 schreef Christian König:
>>>>> Am 10.09.2017 um 09:30 schrieb Maarten Lankhorst:
>>>>> [SNIP]
>>> To be honest that looks rather ugly to me for not much gain.
>>>
>>> Additional to that we loose the optimization I've stolen from the 
>>> wait function.
>> Right now your version does exactly the same as 
>> reservation_object_get_fences_rcu,
>> but with a reservation_object_list instead of a fence array.
>
> Well then please take a closer look again:
>>                 for (i = 0; i < src_list->shared_count; ++i) {
>>                         struct dma_fence *fence;
>>
>>                         fence = rcu_dereference(src_list->shared[i]);
>>                         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
>>                                      &fence->flags))
>>                                 continue;
>>
>>                         if (!dma_fence_get_rcu(fence)) {
>>                                 kfree(dst_list);
>>                                 src_list = rcu_dereference(src->fence);
>>                                 goto retry;
>>                         }
>>
>>                         if (dma_fence_is_signaled(fence)) {
>>                                 dma_fence_put(fence);
>>                                 continue;
>>                         }
>>
>> dst_list->shared[dst_list->shared_count++] = fence;
>>                 }
>
> We only take fences into the new reservation list when they aren't 
> already signaled.
>
> This can't be added to reservation_object_get_fences_rcu() because 
> that would break VM handling on radeon and amdgpu.

What we could do is adding a function to return all fences (including 
the exclusive one) as reservation_object_list() and use that in both the 
wait as well as the copy function.

Regards,
Christian.

>
> Regards,
> Christian.
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