linux-kernel - [PATCH v1 16/16] dma-mapping: Disallow .map_sg operations from returning zero on error

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Message-Id: <20210715164544.6827-17-logang@deltatee.com>
Date:   Thu, 15 Jul 2021 10:45:44 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-parisc@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Stephen Bates <sbates@...thlin.com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: [PATCH v1 16/16] dma-mapping: Disallow .map_sg operations from returning zero on error

Now that all the .map_sg operations have been converted to returning
proper error codes, drop the code to handle a zero return value,
add a warning if a zero is returned and update the comment for the
map_sg operation.

Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
---
 include/linux/dma-map-ops.h | 8 +++-----
 kernel/dma/mapping.c        | 6 +++---
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index eaa969be8284..f299bc1e317b 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -42,11 +42,9 @@ struct dma_map_ops {
 			unsigned long attrs);
 	/*
 	 * map_sg should return a negative error code on error.
-	 * dma_map_sgtable() will return the error code returned and convert
-	 * a zero return (for legacy implementations) into -EINVAL.
-	 *
-	 * dma_map_sg() will always return zero on any negative or zero
-	 * return to satisfy its own calling convention.
+	 * dma_map_sgtable() will return the error code returned by the
+	 * operation and dma_map_sg() will always convert any error to zero
+	 * to satisfy its own calling convention.
 	 */
 	int (*map_sg)(struct device *dev, struct scatterlist *sg, int nents,
 			enum dma_data_direction dir, unsigned long attrs);
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 30f89d244566..978a6a16aaf7 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -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);
+
 	if (ents > 0)
 		debug_dma_map_sg(dev, sg, nents, ents, dir);
 
@@ -251,9 +253,7 @@ int dma_map_sgtable(struct device *dev, struct sg_table *sgt,
 	int nents;
 
 	nents = __dma_map_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs);
-	if (nents == 0)
-		return -EINVAL;
-	else if (nents < 0)
+	if (nents < 0)
 		return nents;
 
 	sgt->nents = nents;
-- 
2.20.1