On Sat, Dec 21, 2013 at 07:42:17AM -0500, Rob Clark wrote:

On Fri, Dec 20, 2013 at 7:43 PM, Colin Cross [off-list ref] wrote:

quoted

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 <redacted>
---
 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.

Care to fix it up?

thanks,

greg k-h