linux-kernel - Re: [PATCH 09/16] dma-debug: add checking for map/unmap

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Message-ID: <20090123102827.GO9466@8bytes.org>
Date:	Fri, 23 Jan 2009 11:28:27 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Joerg Roedel <joerg.roedel@....com>,
	Oliver Neukum <oliver@...kum.org>,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	mingo@...hat.com, ceggers@....de,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH 09/16] dma-debug: add checking for map/unmap_page/single

On Wed, Jan 21, 2009 at 01:17:32AM +0100, Arnd Bergmann wrote:
> On Monday 19 January 2009, Joerg Roedel wrote:
> > Impact: add debug callbacks for dma_{un}map_[page|single]
> 
> In the discussion about "[PATCH] usb/mcs7830: Don't use buffers from
> stack for USB transfers", I have raised the question of whether we can
> add a check for the DMA address being on the stack, I guess this would
> be the right place for it.
> 
> Maybe you can add another check like:
> 
> WARN_ON(is_kernel_stack(page_to_virt(page)));

Good idea. This would be the right place for such a check.

> Unfortunately, I can't think of a way to define a generic is_kernel_stack
> function. On most architectures (all that put thread_info at the top of the
> stack), something like this should work:
> 
> #ifndef is_kernel_stack
> static inline int is_kernel_stack(void *p)
> {
> 	return (unsigned long)p & ~(THREAD_SIZE - 1) == current_thread_info();
> }
> #endif

Hmm, this function is indeed required on all architectures. If you send
a patchset which adds it I will add the check for stack addresses to
this debugging code :)

Joerg

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