On Fri, Feb 7, 2014 at 8:43 AM, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
On Sat, Dec 21, 2013 at 07:42:17AM -0500, Rob Clark wrote:
On Fri, Dec 20, 2013 at 7:43 PM, Colin Cross ccross@android.com 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@android.com
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.
Yeah, I don't like this, it could cause unnecessary reports of problems.
The WARN_ON_ONCE is only if the vmap op returns ERR_PTR, not if it returns NULL. This is designed to catch vmap ops that don't follow the spec, so I would call them necessary reports, but I can take it out if you still disagree.