linux-kernel - Re: [PATCH] asm-generic: dma: Add BUG_ON for uninitialized dma

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Date:	Wed, 20 Jan 2010 11:56:34 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	monstr@...str.eu
CC:	linux-kernel@...r.kernel.org, michal.simek@...alogix.com,
	arnd@...db.de, linux-arch@...r.kernel.org,
	fujita.tomonori@....ntt.co.jp, akpm@...ux-foundation.org,
	mingo@...e.hu
Subject: Re: [PATCH] asm-generic: dma: Add BUG_ON for uninitialized dma_ops

On Wed, Jan 20, 2010 at 11:08:31AM +0100, monstr@...str.eu wrote:
> From: Michal Simek <monstr@...str.eu>
> 
> Check that dma_ops are initialized correctly. Without this
> checking you get kernel fault and you don't know where the problem is.
> 
> Signed-off-by: Michal Simek <monstr@...str.eu>
> ---
>  include/asm-generic/dma-mapping-common.h |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/include/asm-generic/dma-mapping-common.h b/include/asm-generic/dma-mapping-common.h
> index e694263..ca8bc25 100644
> --- a/include/asm-generic/dma-mapping-common.h
> +++ b/include/asm-generic/dma-mapping-common.h
> @@ -15,6 +15,7 @@ static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
>  	dma_addr_t addr;
>  
>  	kmemcheck_mark_initialized(ptr, size);
> +	BUG_ON(!ops);
>  	BUG_ON(!valid_dma_direction(dir));
>  	addr = ops->map_page(dev, virt_to_page(ptr),
>  			     (unsigned long)ptr & ~PAGE_MASK, size,

[...]

> @@ -169,6 +178,7 @@ dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
>  {
>  	struct dma_map_ops *ops = get_dma_ops(dev);
>  
> +	BUG_ON(!ops);
>  	BUG_ON(!valid_dma_direction(dir));
>  	if (ops->sync_sg_for_device)
>  		ops->sync_sg_for_device(dev, sg, nelems, dir);

The more logical place for all these checks would be in get_dma_ops. But
I also question the value of the check. Every dma_ops implementation
that has survived a boot test shouldn't have this bug. So I see no point
in adding extra cycles to every dma-api call.

	Joerg


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