linux-kernel - Re: [PATCH] arm64: Use and error-check DMA_ERROR

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Message-ID: <20141001105659.GF12702@e104818-lin.cambridge.arm.com>
Date:	Wed, 1 Oct 2014 11:56:59 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Will Deacon <will.deacon@....com>
Cc:	Sean Paul <seanpaul@...omium.org>,
	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	"ritesh.harjani@...il.com" <ritesh.harjani@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"olof@...om.net" <olof@...om.net>
Subject: Re: [PATCH] arm64: Use and error-check DMA_ERROR_CODE

On Wed, Oct 01, 2014 at 11:13:23AM +0100, Will Deacon wrote:
> On Tue, Sep 30, 2014 at 09:15:21PM +0100, Sean Paul wrote:
> > This patch replaces the static assignment of ~0 to dma_handle with
> > DMA_ERROR_CODE to be consistent with other platforms.
> > 
> > In addition to that, it also adds a check for DMA_ERROR_CODE before
> > calling __dma_free_coherent with an invalid dma_handle.
> > 
> > Signed-off-by: Sean Paul <seanpaul@...omium.org>
> > ---
> >  arch/arm64/mm/dma-mapping.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> > index 4164c5a..69fd2c4 100644
> > --- a/arch/arm64/mm/dma-mapping.c
> > +++ b/arch/arm64/mm/dma-mapping.c
> > @@ -125,7 +125,7 @@ static void *__dma_alloc_noncoherent(struct device *dev, size_t size,
> >  no_map:
> >  	__dma_free_coherent(dev, size, ptr, *dma_handle, attrs);
> >  no_mem:
> > -	*dma_handle = ~0;
> > +	*dma_handle = DMA_ERROR_CODE;
> >  	return NULL;
> >  }
> >  
> > @@ -136,7 +136,9 @@ static void __dma_free_noncoherent(struct device *dev, size_t size,
> >  	void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> >  
> >  	vunmap(vaddr);
> > -	__dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs);
> > +
> > +	if (dma_handle != DMA_ERROR_CODE)
> > +		__dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs);
> 
> Is it legal to try and free a DMA buffer after a failed allocation? If so, I
> think we need something similar for arch/arm/.

If the allocation failed, we don't even have a vaddr to unmap, so I
don't see the reason for the additional check.

-- 
Catalin
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