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

[Maarten Lankhorst]

Op 11-09-17 om 17:24 schreef 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. 
Yeah, but I don't see the problem with VM, guessing amdgpu_vm_prt_fini.. why would it break if I pruned the signaled fences from the copied list?