vmwgfx leaking bo pins?

[Zack Rusin]

> On Mar 11, 2021, at 17:35, Thomas Hellström (Intel) <thomas_os at shipmail.org> wrote:
> 
> Hi, Zack
> 
> On 3/11/21 10:07 PM, Zack Rusin wrote:
>>> On Mar 11, 2021, at 05:46, Thomas Hellström (Intel) <thomas_os at shipmail.org> wrote:
>>> 
>>> Hi,
>>> 
>>> I tried latest drm-fixes today and saw a lot of these: Fallout from ttm rework?
>> Yes, I fixed this in d1a73c641afd2617bd80bce8b71a096fc5b74b7e it was in drm-misc-next in the drm-misc tree for a while but hasn’t been merged for 5.12.
>> 
>> z
>> 
> Hmm, yes but doesn't that fix trip the ttm_bo_unpin() dma_resv_assert_held(bo->base.resv)?

No, doesn’t seem to. TBH I’m not sure why myself, but it seems to be working fine.

> Taking the reservation to unpin at TTM bo free has always been awkward and that's why vmwgfx and I guess other TTM drivers have been sloppy doing that as TTM never cared. Perhaps TTM could change the pin_count to an atomic and allow unlocked unpinning? still requiring the reservation lock for pin_count transition 0->1, though.

Yea, that’d probably make sense. I think in general just making sure the requirements are consistent and well documented would be great.

> Also, pinning at bo creation in vmwgfx has been to do the equivalent of ttm_bo_init_reserved() (which api was added later). Creating pinned would make the object isolated and allowing the reserve trylock that followed to always succeed. With the introduction of the TTM pin_count, it seems ttm_bo_init_reserved() is used to enable pinned creation which is used to emulate ttm_bo_init_reserved() :)

Yea, we should probably port the vmwgfx code to ttm_bo_init_reserved just to be match the newly established semantics.
z