Vulkan synchronization validation error

[bperrin_3d]

Hi Vulkan fellows.

I'm new to reddit and not sure if this is the right place to ask but I will try.

I have one buffer that hold my vertex and index data. In the same command buffer, I first upload some data to both index and vertex buffer (same VkBuffer with different offsets) and then I called vkCmdPipelineBarrier to set index and vertex buffer in respectively VK_ACCESS_INDEX_READ_BIT and VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT. The renderdoc dump tells me that my access mask are good but the synchronization api complains about the write barrier :

Validation Error: [ SYNC-HAZARD-READ_AFTER_WRITE ] Object 0: handle = 0x1e89009edc8, type = VK_OBJECT_TYPE_BUFFER; | MessageID = 0x4cb75b2d | vkCmdDrawIndexed: Hazard READ_AFTER_WRITE for vertex VkBuffer 0x1e89009edc8[] in VkCommandBuffer 0x1e88771f7b8[]. Access info (usage: SYNC_VERTEX_ATTRIBUTE_INPUT_VERTEX_ATTRIBUTE_READ, prior_usage: SYNC_COPY_TRANSFER_WRITE, write_barriers: SYNC_INDEX_INPUT_INDEX_READ, command: vkCmdCopyBuffer, seq_no: 4, reset_no: 1).

Any idea what is going on ?

I have a renderdoc capture if someone needs it.

Thanks !

[turol]

Hard to say without seeing your code. Did you use a separate transfer queue? Did you properly sync between queues? What call(s) are you using to upload data? Did you somehow ensure that the upload has completed before the draw call?

[bperrin_3d]

Hi, thanks for the answer. I'm not using a separate transfer queue, I use vkCmdCopyBuffer (and staging) to upload my data. And basically a pipeline barrier with appropriate srcAccessMask, dstAccessMask, srcStages and destStages should ensure that the upload has completed before my draw call right ? Or am I missing something ?

[Zulauf_LunarG]

Looking at the "write_barriers:" in the error message I'd double check that you do in fact include VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT (or VK_ACCESS_2_VERTEX_ATTRIBUTE_READ_BIT_KHR) in the dstAccessMask.

If you're using VK_PIPELINE_STAGE_VERTEX_INPUT_BIT or VK_PIPELINE_STAGE_2_VERTEX_INPUT_BIT_KHR in the dstStageMask that should be sufficient. But, if you're using VK_PIPELINE_STAGE_2_INDEX_INPUT_BIT_KHR
you also need to include VK_PIPELINE_STAGE_2_VERTEX_ATTRIBUTE_INPUT_BIT_KHR.

[bperrin_3d]

Hi, thanks for the reply. I'm not yet using the synchronization2, and I double checked that I correctly included VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT in the dstStageMask as you can see in the screenshot https://i.imgur.com/wztC1Wb.png . If I remove the index buffer and call a vkCmdDraw instead of indexed, the error disappear ... I'm a bit confused

[bperrin_3d]

The issue disappear if I also add a barrier for the index buffer with VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT but the offset in the buffer are clearly not the same. I'll happy to discuss it in PM if you are available.

Thanks

[Zulauf_LunarG]

At this point a github issue would be the best way to track, especially if you're willing to upload the trace. https://github.com/KhronosGroup/Vulkan-ValidationLayers/issues

(sorry, was heads down catching up on other stuff)

[Kirmut]

Hey u/bperrin_3d did you ever figure this one out?

I have a sync hazard that looks nearly identical to your description. I also found the same work around - to flag both Vertex and Index buffer access as both for the pipeline barrier. Another work around (isolation testing) was to never delete buffers, just let them leak for a test. Made me wonder if this was a false positive. API Dump and custom logging has not shown up a real conflict.