[PATCH v2 2/3] drm/amdgpu: Allow dma_map_sg() coalescing

[Robin Murphy]

On 25/04/18 21:44, Sinan Kaya wrote:
> On 4/17/2018 5:13 PM, Sinan Kaya wrote:
>> Tested-by: Sinan Kaya <okaya at codeaurora.org>
>>
>> using QDF2400 and XFX Vega64 GPU for the first two patches.
>>
>> ./builddir/tests/amdgpu/amdgpu_test -s 1
>>
>> Suite: Basic Tests
>>    Test: Userptr Test ...passed
>>
>> Userptr Test fails without this patch.
> 
> 
> I'm taking this back. I observed a crash with the HSA applications:

FWIW, was this working before, or is this somewhere new that we're only 
reaching now that pin_userpages can succeed?

> ubuntu at ubuntu:~/amdgpu$_./vectoradd_hip.exe
> [  834.002206] create_process:620
> [  837.413021] Unable to handle kernel NULL pointer dereference at virtual address 00000018

£5 says that's sg_dma_len(NULL), which implies either that something's 
gone horribly wrong with the scatterlist DMA mapping such that the 
lengths don't match, or much more likely that ttm.dma_address is NULL 
and I've missed the tiny subtlety below. Does that fix matters?

Robin.


----->8-----
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index b8ca06ea7d80..6a31229e4611 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -961,7 +961,7 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table 
*sgt, struct page **pages,
  			index++;
  		}

-		if (dma_len == 0) {
+		if (addrs && dma_len == 0) {
  			dma_sg = sg_next(dma_sg);
  			dma_len = sg_dma_len(dma_sg);
  			addr = sg_dma_address(dma_sg);