Hi Roland & vmwgfx maintainers,

Thomas has played around with these annotations on his vmwgfx setup, and found some issues. Apparently in the atomic_commit_tail path when handling the dirty rectangle stuff you acquire a ttm reservation, which is a no-go since it could deadlock with other paths - atomic commits can produce a dma_fence.

This patch here highlights that with the new annotations, and apparently causes a lockdep splat if you go through the dirty rect paths (not sure if it also happens otherwise, Thomas can fill you in with the details).

Can you pls take a look at this? I'm happy to help out with analyzing any lockdep splats. For actual fixes Thomas is better since I don't understand a lot of how drm/vmwgfx works internally.

Cheers, Daniel

On Thu, Jun 4, 2020 at 10:12 AM Daniel Vetter daniel.vetter@ffwll.ch wrote:

I need a canary in a ttm-based atomic driver to make sure the dma_fence_begin/end_signalling annotations actually work.

Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org Cc: linux-rdma@vger.kernel.org Cc: amd-gfx@lists.freedesktop.org Cc: intel-gfx@lists.freedesktop.org Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Christian König christian.koenig@amd.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com

---

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index bdba0bfd6df1..adabfa929f42 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -57,6 +57,7 @@

#include "ivsrcid/ivsrcid_vislands30.h"

+#include <linux/module.h> #include <linux/module.h> #include <linux/moduleparam.h> #include <linux/version.h> @@ -7320,6 +7321,9 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state) struct drm_connector_state *old_con_state, *new_con_state; struct dm_crtc_state *dm_old_crtc_state, *dm_new_crtc_state; int crtc_disable_count = 0;

•   bool fence_cookie;
  

•   fence_cookie = dma_fence_begin_signalling();
  
    drm_atomic_helper_update_legacy_modeset_state(dev, state);
  
  

@@ -7600,6 +7604,8 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state) /* Signal HW programming completion */ drm_atomic_helper_commit_hw_done(state);

•   dma_fence_end_signalling(fence_cookie);
  

•   if (wait_for_vblank)
            drm_atomic_helper_wait_for_flip_done(dev, state);
  
  

-- 2.26.2