On 2021-11-12 16:03, Christian König wrote: > Am 12.11.21 um 15:30 schrieb Michel Dänzer: >> On 2021-11-12 15:29, Michel Dänzer wrote: >>> On 2021-11-12 13:47, Christian König wrote: >>>> Anyway this unfortunately turned out to be work for Harray and Nicholas. In detail it's about this bug report here: https://bugzilla.kernel.org/show_bug.cgi?id=214621 >>>> >>>> Lang was able to reproduce the issue and narrow it down to the pin in amdgpu_display_crtc_page_flip_target(). >>>> >>>> In other words we somehow have an unbalanced pinning of the scanout buffer in DC. >>> DC doesn't use amdgpu_display_crtc_page_flip_target AFAICT. The corresponding pin with DC would be in dm_plane_helper_prepare_fb, paired with the unpin in >>> dm_plane_helper_cleanup_fb. >>> >>> >>> With non-DC, the pin in amdgpu_display_crtc_page_flip_target is paired with the unpin in dm_plane_helper_cleanup_fb >> This should say amdgpu_display_unpin_work_func. > > Ah! So that is the classic (e.g. non atomic) path? Presumably. >>> & dce_v*_crtc_disable. One thing I notice is that the pin is guarded by if (!adev->enable_virtual_display), but the unpins seem unconditional. So could this be about virtual display, and the problem is actually trying to unpin a BO that was never pinned? > > Nope, my educated guess is rather that we free up the BO before amdgpu_display_unpin_work_func is called. > > E.g. not pin unbalance, but rather use after free. amdgpu_display_crtc_page_flip_target calls amdgpu_bo_ref(work->old_abo), and amdgpu_display_unpin_work_func calls amdgpu_bo_unref(&work->old_abo) only after amdgpu_bo_unpin. So what you describe could only happen if there's an imbalance elsewhere such that amdgpu_bo_unref is called more often than amdgpu_bo_ref, or maybe if amdgpu_bo_reserve fails in amdgpu_display_unpin_work_func (in which case the "failed to reserve buffer after flip" error message should appear in dmesg). -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and Xwayland developer
