Re: [PATCH 03/15] dma-buf & drm/amdgpu: remove dma_resv workaround

Zack Rusin
2022-04-21T21:13:44Z

On Thu, 2022-04-21 at 12:17 +0200, Christian König wrote:
> ⚠ External Email
>
> Am 20.04.22 um 21:28 schrieb Zack Rusin:
> > [SNIP]
> > > To figure out what it is could you try the following code
> > > fragment:
> > >
> > > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_validation.c
> > > b/drivers/gpu/drm/vmwgfx/vmwgfx_validation.c
> > > index f46891012be3..a36f89d3f36d 100644
> > > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_validation.c
> > > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_validation.c
> > > @@ -288,7 +288,7 @@ int vmw_validation_add_bo(struct
> > > vmw_validation_context *ctx,
> > >                   val_buf->bo = ttm_bo_get_unless_zero(&vbo-
> > > >base);
> > >                   if (!val_buf->bo)
> > >                           return -ESRCH;
> > > -               val_buf->num_shared = 0;
> > > +               val_buf->num_shared = 16;
> > >                   list_add_tail(&val_buf->head, &ctx->bo_list);
> > >                   bo_node->as_mob = as_mob;
> > >                   bo_node->cpu_blit = cpu_blit;
> > Fails the same BUG_ON with num_fences and max_fences == 0.
>
> Thanks for testing this.
>
> So the buffer object is not reserved through
> vmw_validation_bo_reserve(), but comes from somewhere else.
> Unfortunately I absolutely can't find where that's coming from.
>
> Do you have some documentation howto setup vmwgfx? E.g. sample VM
> which
> I can download somewhere etc..

I don't have an external machine to upload it to. Getting an external
machine to run Mesa CI on has been on our todo for a while, so I'll try
to setup something next week.

The issue here seems to be that vmwgfx always had some buffers that
didn't immediately go through vmw_validation_bo_reserve. What's
happening is that in vmwgfx_execbuf.c in vmw_execbuf_process we call
vmw_validation_bo_reserve and after it we call
vmw_validation_res_validate. Inside vmw_validation_res_validate (in
vmwgfx_validation.c) we call vmw_resource_validate, which calls
vmw_resource_do_validate . vmw_resource_do_validate has this code "ret
= func->create(res);" which is an issue for vmwgfx_cotable.c . The
func->create for cotable's is vmw_cotable_create which calls
vmw_cotable_resize which creates, reserves and validates a new bo.

In short a new bo is created in vmw_cotable_resize between
ttm_eu_reserve_buffers and ttm_eu_fence_buffer_objects calls.

z