Amdgpu module is references even after unbinding the vtcon

[Thomas Zimmermann]

Hi

Am 24.01.23 um 15:12 schrieb Christian König:
> Hi Thomas,
> 
> we ran into a problem with the general fbcon/fbdev implementation and 
> though that you might have some idea.
> 
> What happens is the following:
> 1. We load amdgpu and get our normal fbcon.
> 2. fbcon allocates a dump BO as backing store for the console.
> 3. GDM/X/Applications start, new framebuffers are created BOs imported, 
> exported etc...
> 4. Somehow X or GDM iterated over all the framebuffer objects the 
> kernels knows about and export them as DMA-buf.
> 5. Application/X/GDM are stopped, handles closed, framebuffers released 
> etc...
> 6. We unbind vtcon.
> 
> At this point the amdgpu module usually has a reference count of 0 and 
> can be unloaded, but since GDM/X/Whoever iterated over all the known 
> framebuffers and exported them as DMA-buf (for whatever reason idk) we 
> now still have an exported DMA-buf and with it a reference to the module.
> 
> Any idea how we could prevent that?

No real clue, sorry.

But does it change if you use a shadow buffer on top of the amdgpu BO? 
Set prefer_shadow_fbdev = 1. [1]   I once tried to run generic fbdev 
without prefer_shadow_fbdev and it never worked. I suspected that some 
reference counting got wrong, but could never pin it down.  Maybe your 
issue is similar.

That said, generic fbdev is not so super-optimal for TTM-based drivers. 
I'm working on improving that, but it's not there yet.

Best regards
Thomas


[1] 
https://elixir.bootlin.com/linux/v6.0/source/include/drm/drm_mode_config.h#L890

> 
> Thanks,
> Christian.

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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