[PATCH 5/8] drm/vmwgfx: partially revert "Adapt validation code for reference-free lookups"

[Thomas Hellström]

On Tue, 2024-07-23 at 14:17 +0200, Christian König wrote:
> This reverts commit 64ad2abfe9a628ce79859d072704bd1ef7682044.
> 
> To me it looks like this functionality was never actually used. At
> least
> I can't find any protection in vmw_bo_free().
> 
> Signed-off-by: Christian König <christian.koenig at amd.com>
> Cc: Zack Rusin <zack.rusin at broadcom.com>
> Cc: Broadcom internal kernel review list
> <bcm-kernel-feedback-list at broadcom.com>

IIRC the reference-free lookups were used to avoid the extensive
referencing and unreferencing during the command stream parsing by
means of rcu protection, so when vmw_validation_add() was called the bo
pointer might have been only rcu-protected.

>From a brief look this looks like it's been changed with the gem
rewrite and if so, this patch should probably be safe.

/Thomas

> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_validation.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_validation.c
> b/drivers/gpu/drm/vmwgfx/vmwgfx_validation.c
> index e7625b3f71e0..e11837e484aa 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_validation.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_validation.c
> @@ -262,7 +262,8 @@ int vmw_validation_add_bo(struct
> vmw_validation_context *ctx,
>  				bo_node->hash.key);
>  		}
>  		val_buf = &bo_node->base;
> -		val_buf->bo = ttm_bo_get_unless_zero(&vbo->tbo);
> +		vmw_bo_reference(vbo);
> +		val_buf->bo = &vbo->tbo;
>  		if (!val_buf->bo)
>  			return -ESRCH;
>  		val_buf->num_shared = 0;
> @@ -656,7 +657,7 @@ void vmw_validation_unref_lists(struct
> vmw_validation_context *ctx)
>  	struct vmw_validation_res_node *val;
>  
>  	list_for_each_entry(entry, &ctx->bo_list, base.head) {
> -		ttm_bo_put(entry->base.bo);
> +		drm_gem_object_put(&entry->base.bo->base);
>  		entry->base.bo = NULL;
>  	}
>