Re: [PATCH 4/7] drm/ttm: move LRU walk defines into new internal header

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Tue, Aug 27, 2024 at 06:52:13PM +0200, Daniel Vetter wrote:
> On Thu, Aug 22, 2024 at 03:19:29PM +0200, Christian König wrote:
> > Completely agree that this is complicated, but I still don't see the need
> > for it.
> > 
> > Drivers just need to use pm_runtime_get_if_in_use() inside the shrinker and
> > postpone all hw activity until resume.
> 
> Not good enough, at least long term I think. Also postponing hw activity
> to resume doesn't solve the deadlock issue, if you still need to grab ttm
> locks on resume.

Pondered this specific aspect some more, and I think you still have a race
here (even if you avoid the deadlock): If the condiditional rpm_get call
fails there's no guarantee that the device will suspend/resume and clean
up the GART mapping. The race gets a bit smaller if you use
pm_runtime_get_if_active(), but even then you might catch it right when
resume almost finished.

That means we'll have ttm bo hanging around with GART allocations/mappings
which aren't actually valid anymore (since they might escape the cleanup
upon resume due to the race). That doesn't feel like a solid design
either.
-Sima
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch