Re: [PATCH v5] drm/test: add a test suite for GEM objects backed by shmem

[Marco Pagani]

On 2024-02-22 16:52, Guenter Roeck wrote:
> Hi Marco,
> 
> On 2/22/24 07:32, Marco Pagani wrote:
>>
>>
>> On 2024-02-18 16:49, Guenter Roeck wrote:
>>> Hi,
>>>
>>> On Thu, Nov 30, 2023 at 06:14:16PM +0100, Marco Pagani wrote:
>>>> This patch introduces an initial KUnit test suite for GEM objects
>>>> backed by shmem buffers.
>>>>
>>>> Suggested-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
>>>> Signed-off-by: Marco Pagani <marpagan@xxxxxxxxxx>
>>>
>>> When running this in qemu, I get lots of warnings backtraces in the drm
>>> core.
>>>
>>> WARNING: CPU: 0 PID: 1341 at drivers/gpu/drm/drm_gem_shmem_helper.c:327
>>> WARNING: CPU: 0 PID: 1341 at drivers/gpu/drm/drm_gem_shmem_helper.c:173
>>> WARNING: CPU: 0 PID: 1341 at drivers/gpu/drm/drm_gem_shmem_helper.c:385
>>> WARNING: CPU: 0 PID: 1341 at drivers/gpu/drm/drm_gem_shmem_helper.c:211
>>> WARNING: CPU: 0 PID: 1345 at kernel/dma/mapping.c:194
>>> WARNING: CPU: 0 PID: 1347 at drivers/gpu/drm/drm_gem_shmem_helper.c:429
>>> WARNING: CPU: 0 PID: 1349 at drivers/gpu/drm/drm_gem_shmem_helper.c:445
>>>
>>> It looks like dma_resv_assert_held() asserts each time it is executed.
>>> The backtrace in kernel/dma/mapping.c is triggered by
>>>     if (WARN_ON_ONCE(!dev->dma_mask))
>>>         return 0;
>>> in __dma_map_sg_attrs().
>>>
>>> Is this a possible problem in the test code, or can it be caused by
>>> some limitations or bugs in the qemu emulation ? If so, do you have any
>>> thoughts or ideas what those limitations / bugs might be ?
>>
>> Hi Guenter,
>>
>> Thanks for reporting this issue. As you correctly noted, the warnings appear to
>> be caused by the dma_mask in the mock device being uninitialized. I'll send a
>> patch to fix it soon.
>>
> 
> Thanks a lot for the update.
> 
> In this context, the TTM unit tests fail as well in qemu, with worse result:
> It seems there is some bad cleanup after a failed test case, causing list
> corruptions in the drm core and ultimately a crash. I don't know if this
> is also caused by the missing dma_mask initialization.
> 

That's interesting. Which --arch argument are you using to run the
tests with QEMU?
Thanks,
Marco