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* [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg
@ 2019-05-29  8:15 Nathan Chancellor
  2019-05-29 10:12 ` Robin Murphy
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Nathan Chancellor @ 2019-05-29  8:15 UTC (permalink / raw)
  To: Joerg Roedel, Christoph Hellwig
  Cc: Robin Murphy, iommu, linux-kernel, Nick Desaulniers,
	clang-built-linux, Nathan Chancellor

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.

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@gmail.com>
---
 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);
 
 	/*
-- 
2.22.0.rc1


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg
  2019-05-29  8:15 [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg Nathan Chancellor
@ 2019-05-29 10:12 ` Robin Murphy
  2019-05-29 12:14 ` Christoph Hellwig
  2019-06-03 10:39 ` Joerg Roedel
  2 siblings, 0 replies; 4+ messages in thread
From: Robin Murphy @ 2019-05-29 10:12 UTC (permalink / raw)
  To: Nathan Chancellor, Joerg Roedel, Christoph Hellwig
  Cc: iommu, linux-kernel, Nick Desaulniers, clang-built-linux

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@arm.com>

> 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@gmail.com>
> ---
>   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);
>   
>   	/*
> 

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg
  2019-05-29  8:15 [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg Nathan Chancellor
  2019-05-29 10:12 ` Robin Murphy
@ 2019-05-29 12:14 ` Christoph Hellwig
  2019-06-03 10:39 ` Joerg Roedel
  2 siblings, 0 replies; 4+ messages in thread
From: Christoph Hellwig @ 2019-05-29 12:14 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: Joerg Roedel, Christoph Hellwig, Robin Murphy, iommu,
	linux-kernel, Nick Desaulniers, clang-built-linux

Ooops, thanks for catching this:

Reviewed-by: Christoph Hellwig <hch@lst.de>

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg
  2019-05-29  8:15 [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg Nathan Chancellor
  2019-05-29 10:12 ` Robin Murphy
  2019-05-29 12:14 ` Christoph Hellwig
@ 2019-06-03 10:39 ` Joerg Roedel
  2 siblings, 0 replies; 4+ messages in thread
From: Joerg Roedel @ 2019-06-03 10:39 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: Christoph Hellwig, Robin Murphy, iommu, linux-kernel,
	Nick Desaulniers, clang-built-linux

On Wed, May 29, 2019 at 01:15:32AM -0700, Nathan Chancellor wrote:
> 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@gmail.com>
> ---
>  drivers/iommu/dma-iommu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thanks.

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2019-06-03 10:39 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2019-05-29  8:15 [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg Nathan Chancellor
2019-05-29 10:12 ` Robin Murphy
2019-05-29 12:14 ` Christoph Hellwig
2019-06-03 10:39 ` Joerg Roedel

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