Re: [PATCH] dma-buf: avoid using IS_ERR_OR_NULL

From: Rob Clark
Date: Sat Dec 21 2013 - 07:49:43 EST

On Fri, Dec 20, 2013 at 7:43 PM, Colin Cross <ccross@xxxxxxxxxxx> wrote:
> dma_buf_map_attachment and dma_buf_vmap can return NULL or
> ERR_PTR on a error. This encourages a common buggy pattern in
> callers:
> sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
> if (IS_ERR_OR_NULL(sgt))
> return PTR_ERR(sgt);
>
> This causes the caller to return 0 on an error. IS_ERR_OR_NULL
> is almost always a sign of poorly-defined error handling.
>
> This patch converts dma_buf_map_attachment to always return
> ERR_PTR, and fixes the callers that incorrectly handled NULL.
> There are a few more callers that were not checking for NULL
> at all, which would have dereferenced a NULL pointer later.
> There are also a few more callers that correctly handled NULL
> and ERR_PTR differently, I left those alone but they could also
> be modified to delete the NULL check.
>
> This patch also converts dma_buf_vmap to always return NULL.
> All the callers to dma_buf_vmap only check for NULL, and would
> have dereferenced an ERR_PTR and panic'd if one was ever
> returned. This is not consistent with the rest of the dma buf
> APIs, but matches the expectations of all of the callers.
>
> Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx>
> ---
> drivers/base/dma-buf.c | 18 +++++++++++-------
> drivers/gpu/drm/drm_prime.c | 2 +-
> drivers/gpu/drm/exynos/exynos_drm_dmabuf.c | 2 +-
> drivers/media/v4l2-core/videobuf2-dma-contig.c | 2 +-
> 4 files changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
> index 1e16cbd61da2..cfe1d8bc7bb8 100644
> --- a/drivers/base/dma-buf.c
> +++ b/drivers/base/dma-buf.c
> @@ -251,9 +251,8 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
> * @dmabuf: [in] buffer to attach device to.
> * @dev: [in] device to be attached.
> *
> - * Returns struct dma_buf_attachment * for this attachment; may return negative
> - * error codes.
> - *
> + * Returns struct dma_buf_attachment * for this attachment; returns ERR_PTR on
> + * error.
> */
> struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> struct device *dev)
> @@ -319,9 +318,8 @@ EXPORT_SYMBOL_GPL(dma_buf_detach);
> * @attach: [in] attachment whose scatterlist is to be returned
> * @direction: [in] direction of DMA transfer
> *
> - * Returns sg_table containing the scatterlist to be returned; may return NULL
> - * or ERR_PTR.
> - *
> + * Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
> + * on error.
> */
> struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> enum dma_data_direction direction)
> @@ -334,6 +332,8 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> return ERR_PTR(-EINVAL);
>
> sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> + if (!sg_table)
> + sg_table = ERR_PTR(-ENOMEM);
>
> return sg_table;
> }
> @@ -544,6 +544,8 @@ EXPORT_SYMBOL_GPL(dma_buf_mmap);
> * These calls are optional in drivers. The intended use for them
> * is for mapping objects linear in kernel space for high use objects.
> * Please attempt to use kmap/kunmap before thinking about these interfaces.
> + *
> + * Returns NULL on error.
> */
> void *dma_buf_vmap(struct dma_buf *dmabuf)
> {
> @@ -566,7 +568,9 @@ void *dma_buf_vmap(struct dma_buf *dmabuf)
> BUG_ON(dmabuf->vmap_ptr);
>
> ptr = dmabuf->ops->vmap(dmabuf);
> - if (IS_ERR_OR_NULL(ptr))
> + if (WARN_ON_ONCE(IS_ERR(ptr)))

since vmap is optional, the WARN_ON might be a bit strong.. although
it would be a bit strange for an exporter to supply a vmap fxn which
always returned NULL, not sure about that. Just thought I'd mention
it in case anyone else had an opinion about that.

But either way:

Reviewed-by: Rob Clark <robdclark@xxxxxxxxx>


> + ptr = NULL;
> + if (!ptr)
> goto out_unlock;
>
> dmabuf->vmap_ptr = ptr;
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 56805c39c906..bb516fdd195d 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -471,7 +471,7 @@ struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
> get_dma_buf(dma_buf);
>
> sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
> - if (IS_ERR_OR_NULL(sgt)) {
> + if (IS_ERR(sgt)) {
> ret = PTR_ERR(sgt);
> goto fail_detach;
> }
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dmabuf.c b/drivers/gpu/drm/exynos/exynos_drm_dmabuf.c
> index 59827cc5e770..c786cd4f457b 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_dmabuf.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_dmabuf.c
> @@ -224,7 +224,7 @@ struct drm_gem_object *exynos_dmabuf_prime_import(struct drm_device *drm_dev,
> get_dma_buf(dma_buf);
>
> sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
> - if (IS_ERR_OR_NULL(sgt)) {
> + if (IS_ERR(sgt)) {
> ret = PTR_ERR(sgt);
> goto err_buf_detach;
> }
> diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
> index 33d3871d1e13..880be0782dd9 100644
> --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
> @@ -719,7 +719,7 @@ static int vb2_dc_map_dmabuf(void *mem_priv)
>
> /* get the associated scatterlist for this buffer */
> sgt = dma_buf_map_attachment(buf->db_attach, buf->dma_dir);
> - if (IS_ERR_OR_NULL(sgt)) {
> + if (IS_ERR(sgt)) {
> pr_err("Error getting dmabuf scatterlist\n");
> return -EINVAL;
> }
> --
> 1.8.5.1
>
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