On 2021-11-15 12:31, Lang Yu wrote: > On Mon, Nov 15, 2021 at 10:49:39AM +0100, Michel DDDnzer wrote: >> On 2021-11-15 10:04, Lang Yu wrote: >>> On Mon, Nov 15, 2021 at 09:38:47AM +0100, Michel DDDnzer wrote: >>>> On 2021-11-15 07:41, Lang Yu wrote: >>>>> On Fri, Nov 12, 2021 at 05:10:27PM +0100, Michel DDDnzer wrote: >>>>>> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D214621&data=04%7C01%7CLang.Yu%40amd.com%7Cee54c4d055d040ef9f8b08d9a81d3eb9%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637725665833112900%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=7nwIYd1um420XHVpOzeIvz37%2FLQqHF%2F6aRKfzgxUTnM%3D&reserved=0 >>>>>>>>>> >>>>>>>>>> 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). >>>>> >>>>> >>>>> Actually, each call to amdgpu_display_crtc_page_flip_target() will >>>>> >>>>> 1, init a work(amdgpu_display_unpin_work_func) to unpin an old buffer >>>>> (crtc->primary->fb), the work will be queued in dce_vX_0_pageflip_irq(). >>>>> >>>>> 2, pin a new buffer, assign it to crtc->primary->fb. But how to unpin it? >>>>> Next call. >>>>> >>>>> The problem is the pinned buffer of last call to >>>>> amdgpu_display_crtc_page_flip_target() is not unpinned. >>>> >>>> It's unpinned in dce_v*_0_crtc_disable. >>> >>> I just found crtc->primary->fb is NULL when came in dce_v*_0_crtc_disable(). >>> So it's not unpinned... >> >> __drm_helper_disable_unused_functions sets crtc->primary->fb = NULL only after calling crtc_funcs->disable. Maybe this path can get hit for a CRTC which was already disabled, in which case crtc->primary->fb == NULL in dce_v*_0_crtc_disable is harmless. >> >> Have you checked for the issue I described below? Should be pretty easy to catch. >> >> >>>> I think I've found the problem though: dce_v*_0_crtc_do_set_base pin the BO from target_fb unconditionally, but unpin the BO from the fb parameter only if it's different from the former. So if they're the same, the BO's pin count is incremented by 1. > > Form my observations, amdgpu_bo_unpin() in dce_v*_0_crtc_disable() is > never called. It would be expected to happen when the screen turns off, e.g. due to DPMS. > Though a single call to dce_v*_0_crtc_do_set_base() will > only pin the BO, I found it will be unpinned in next call to > dce_v*_0_crtc_do_set_base(). Yeah, that's the normal case when the new BO is different from the old one. To catch the case I described, try something like diff --git a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c index 18a7b3bd633b..5726bd87a355 100644 --- a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c +++ b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c @@ -1926,6 +1926,7 @@ static int dce_v11_0_crtc_do_set_base(struct drm_crtc *crtc, return r; if (!atomic) { + WARN_ON_ONCE(target_fb == fb); r = amdgpu_bo_pin(abo, AMDGPU_GEM_DOMAIN_VRAM); if (unlikely(r != 0)) { amdgpu_bo_unreserve(abo); -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and Xwayland developer
