Amdgpu module is references even after unbinding the vtcon

[Thomas Zimmermann]

Hi

Am 24.01.23 um 17:36 schrieb Alex Deucher:
> On Tue, Jan 24, 2023 at 11:15 AM Thomas Zimmermann <tzimmermann at suse.de> wrote:
>>
>> 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.
> 
> Is that equivalent to setting mode_config.prefer_shadow = 1?  If so,
> we already do that.

Yes it is, unfortunately.

Best regards
Thomas

> 
> Alex
> 
>>
>> 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

-- 
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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