On 2021-07-16 07:33, Christoph Hellwig wrote:

On Thu, Jul 15, 2021 at 10:45:44AM -0600, Logan Gunthorpe wrote:

quoted

@@ -194,6 +194,8 @@ static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
  	else
  		ents = ops->map_sg(dev, sg, nents, dir, attrs);
  
+	WARN_ON_ONCE(ents == 0);

Turns this into a negative error code while we're at it, just to keep
the callers sane?

Right, by this point returning the 0 would pass through 
dma_map_sg_attrs() OK, but AFAICS dma_map_sgtable() would now get 
confused and return success but with sgt->nents = 0. Coercing it to an 
error code (which dma_map_sg_attrs() would then just change right back) 
seems sensible for the sake of easy robustness.

Robin.