Questions about KMS flip

[Christian König]

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?

>> & 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.

Regards,
Christian.