Re: [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg
From: Robin Murphy
Date: Wed May 29 2019 - 06:15:47 EST
On 29/05/2019 09:15, Nathan Chancellor wrote:
Clang warns:
drivers/iommu/dma-iommu.c:897:6: warning: logical not is only applied to
the left hand side of this comparison [-Wlogical-not-parentheses]
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
^ ~~
drivers/iommu/dma-iommu.c:897:6: note: add parentheses after the '!' to
evaluate the comparison first
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
^
( )
drivers/iommu/dma-iommu.c:897:6: note: add parentheses around left hand
side expression to silence this warning
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
^
( )
1 warning generated.
Judging from the rest of the commit and the conditional in
iommu_dma_map_sg, either
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
or
if ((attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
was intended, not a combination of the two.
I personally think that the former is easier to understand so use that.
Good catch, thanks Nathan. Looks like this was an unintentional mangling
while ratifying the couple of odd "x == 0" instances to "!x" in the
move. The effective double-negation is not what we want at all.
Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
Fixes: 06d60728ff5c ("iommu/dma: move the arm64 wrappers to common code")
Link: https://github.com/ClangBuiltLinux/linux/issues/497
Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
---
drivers/iommu/dma-iommu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 0cd49c2d3770..0dee374fc64a 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -894,7 +894,7 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
struct scatterlist *tmp;
int i;
- if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
+ if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
/*