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

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Message-Id: <200901210117.33153.arnd@arndb.de>
Date:	Wed, 21 Jan 2009 01:17:32 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	fujita.tomonori@....ntt.co.jp, dwmw2@...radead.org,
	iommu@...ts.linux-foundation.org,
	David Miller <davem@...emloft.net>,
	Oliver Neukum <oliver@...kum.org>, ceggers@....de
Subject: Re: [PATCH 09/16] dma-debug: add checking for map/unmap_page/single

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)));

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

	Arnd <><
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