Re: [PATCH] drm/shmem-helpers: Simplify dma-buf importing

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 29 May 2020 16:05:42 +0200
Daniel Vetter <daniel.vetter@ffwll.ch> wrote:

> - Ditch the ->pages array
> - Make it a private gem bo, which means no shmem object, which means
>   fireworks if anyone calls drm_gem_object_get_pages. But we've just
>   made sure that's all covered.
> 
> v2: Rebase
> 
> v3: I forgot to remove the page_count mangling from the free path too.
> Noticed by Boris while testing.
> 
> Cc: Boris Brezillon <boris.brezillon@collabora.com>

Tested-by: Boris Brezillon <boris.brezillon@collabora.com>

> Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Noralf Trønnes <noralf@tronnes.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 60 ++++++++++----------------
>  1 file changed, 23 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 06cee8e97d27..f750063968ef 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -35,22 +35,12 @@ static const struct drm_gem_object_funcs drm_gem_shmem_funcs = {
>  	.mmap = drm_gem_shmem_mmap,
>  };
>  
> -/**
> - * drm_gem_shmem_create - Allocate an object with the given size
> - * @dev: DRM device
> - * @size: Size of the object to allocate
> - *
> - * This function creates a shmem GEM object.
> - *
> - * Returns:
> - * A struct drm_gem_shmem_object * on success or an ERR_PTR()-encoded negative
> - * error code on failure.
> - */
> -struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size)
> +static struct drm_gem_shmem_object *
> +__drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private)
>  {
>  	struct drm_gem_shmem_object *shmem;
>  	struct drm_gem_object *obj;
> -	int ret;
> +	int ret = 0;
>  
>  	size = PAGE_ALIGN(size);
>  
> @@ -64,7 +54,10 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
>  	if (!obj->funcs)
>  		obj->funcs = &drm_gem_shmem_funcs;
>  
> -	ret = drm_gem_object_init(dev, obj, size);
> +	if (private)
> +		drm_gem_private_object_init(dev, obj, size);
> +	else
> +		ret = drm_gem_object_init(dev, obj, size);
>  	if (ret)
>  		goto err_free;
>  
> @@ -96,6 +89,21 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
>  
>  	return ERR_PTR(ret);
>  }
> +/**
> + * drm_gem_shmem_create - Allocate an object with the given size
> + * @dev: DRM device
> + * @size: Size of the object to allocate
> + *
> + * This function creates a shmem GEM object.
> + *
> + * Returns:
> + * A struct drm_gem_shmem_object * on success or an ERR_PTR()-encoded negative
> + * error code on failure.
> + */
> +struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size)
> +{
> +	return __drm_gem_shmem_create(dev, size, false);
> +}
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
>  
>  /**
> @@ -113,9 +121,7 @@ void drm_gem_shmem_free_object(struct drm_gem_object *obj)
>  	WARN_ON(shmem->vmap_use_count);
>  
>  	if (obj->import_attach) {
> -		shmem->pages_use_count--;
>  		drm_prime_gem_destroy(obj, shmem->sgt);
> -		kvfree(shmem->pages);
>  	} else {
>  		if (shmem->sgt) {
>  			dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
> @@ -371,7 +377,7 @@ drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
>  	struct drm_gem_shmem_object *shmem;
>  	int ret;
>  
> -	shmem = drm_gem_shmem_create(dev, size);
> +	shmem = __drm_gem_shmem_create(dev, size, true);
>  	if (IS_ERR(shmem))
>  		return shmem;
>  
> @@ -695,36 +701,16 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
>  				    struct sg_table *sgt)
>  {
>  	size_t size = PAGE_ALIGN(attach->dmabuf->size);
> -	size_t npages = size >> PAGE_SHIFT;
>  	struct drm_gem_shmem_object *shmem;
> -	int ret;
>  
>  	shmem = drm_gem_shmem_create(dev, size);
>  	if (IS_ERR(shmem))
>  		return ERR_CAST(shmem);
>  
> -	shmem->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
> -	if (!shmem->pages) {
> -		ret = -ENOMEM;
> -		goto err_free_gem;
> -	}
> -
> -	ret = drm_prime_sg_to_page_addr_arrays(sgt, shmem->pages, NULL, npages);
> -	if (ret < 0)
> -		goto err_free_array;
> -
>  	shmem->sgt = sgt;
> -	shmem->pages_use_count = 1; /* Permanently pinned from our point of view */
>  
>  	DRM_DEBUG_PRIME("size = %zu\n", size);
>  
>  	return &shmem->base;
> -
> -err_free_array:
> -	kvfree(shmem->pages);
> -err_free_gem:
> -	drm_gem_object_put(&shmem->base);
> -
> -	return ERR_PTR(ret);
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);

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