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

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Message-ID: <20141001101323.GB2587@arm.com>
Date:	Wed, 1 Oct 2014 11:13:23 +0100
From:	Will Deacon <will.deacon@....com>
To:	Sean Paul <seanpaul@...omium.org>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"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

Hi Sean,

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/.

Will
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