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@redhat.com Signed-off-by: Marco Pagani marpagan@redhat.com

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.

Thanks, Guenter