Re: [Intel-gfx] [PATCH 01/25] dma-fence: basic lockdep annotations

[Daniel Stone <daniel@fooishbar.org>]

Hi,

On Wed, 8 Jul 2020 at 16:13, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> On Wed, Jul 8, 2020 at 4:57 PM Christian König <christian.koenig@amd.com> wrote:
> > Could we merge this controlled by a separate config option?
> >
> > This way we could have the checks upstream without having to fix all the
> > stuff before we do this?
>
> Since it's fully opt-in annotations nothing blows up if we don't merge
> any annotations. So we could start merging the first 3 patches. After
> that the fun starts ...
>
> My rough idea was that first I'd try to tackle display, thus far
> there's 2 actual issues in drivers:
> - amdgpu has some dma_resv_lock in commit_tail, plus a kmalloc. I
> think those should be fairly easy to fix (I'd try a stab at them even)
> - vmwgfx has a full on locking inversion with dma_resv_lock in
> commit_tail, and that one is functional. Not just reading something
> which we can safely assume to be invariant anyway (like the tmz flag
> for amdgpu, or whatever it was).
>
> I've done a pile more annotations patches for other atomic drivers
> now, so hopefully that flushes out any remaining offenders here. Since
> some of the annotations are in helper code worst case we might need a
> dev->mode_config.broken_atomic_commit flag to disable them. At least
> for now I have 0 plans to merge any of these while there's known
> unsolved issues. Maybe if some drivers take forever to get fixed we
> can then apply some duct-tape for the atomic helper annotation patch.
> Instead of a flag we can also copypasta the atomic_commit_tail hook,
> leaving the annotations out and adding a huge warning about that.

How about an opt-in drm_driver DRIVER_DEADLOCK_HAPPY flag? At first
this could just disable the annotations and nothing else, but as we
see the annotations gaining real-world testing and maturity, we could
eventually make it taint the kernel.

Cheers,
Daniel