linux-kernel - Re: [PATCH 15/16] dma-debug: x86 architecture bindings

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Date:	Wed, 25 Feb 2009 12:14:19 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	dwmw2@...radead.org, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 15/16] dma-debug: x86 architecture bindings

On Sun, Feb 22, 2009 at 03:50:46PM +0900, FUJITA Tomonori wrote:
> On Mon, 19 Jan 2009 15:47:02 +0100
> Joerg Roedel <joerg.roedel@....com> wrote:
> 
> > Impact: make use of DMA-API debugging code in x86
> > 
> > Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> > ---
> >  arch/x86/Kconfig                   |    1 +
> >  arch/x86/include/asm/dma-mapping.h |   45 +++++++++++++++++++++++++++++++----
> >  arch/x86/kernel/pci-dma.c          |    6 ++++
> >  3 files changed, 46 insertions(+), 6 deletions(-)
> 
> (snip)
> 
> >  static inline int
> > @@ -79,9 +86,13 @@ dma_map_sg(struct device *hwdev, struct scatterlist *sg,
> >  	   int nents, enum dma_data_direction dir)
> >  {
> >  	struct dma_map_ops *ops = get_dma_ops(hwdev);
> > +	int ents;
> >  
> >  	BUG_ON(!valid_dma_direction(dir));
> > -	return ops->map_sg(hwdev, sg, nents, dir, NULL);
> > +	ents = ops->map_sg(hwdev, sg, nents, dir, NULL);
> > +	debug_dma_map_sg(hwdev, sg, ents, dir);
> 
> The way to handle dma_map_sg and dma_unmap_sg looks wrong.
> 
> ents could be smaller than nents here with IOMMU implementations that
> merge several sg entries into one.
> 
> 
> > +	return ents;
> >  }
> >  
> >  static inline void
> > @@ -91,6 +102,7 @@ dma_unmap_sg(struct device *hwdev, struct scatterlist *sg, int nents,
> >  	struct dma_map_ops *ops = get_dma_ops(hwdev);
> >  
> >  	BUG_ON(!valid_dma_direction(dir));
> > +	debug_dma_unmap_sg(hwdev, sg, nents, dir);
> 
> Here the nents is the same one you passed into dma_map_sg call. It is
> not the value returned from dma_map_sg (see DMA-mapping.txt).
> 
> So we call check_unmap for entries that we didn't call add_dma_entry
> for on dma_map_sg. These entries are not initialized so we could get any
> kinds of warnings from check_unmap.

Ah, you are right. I mis-read the documentation. I will fix this in the
next release.

Joerg


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