From: Arnd Bergmann <arnd@arndb.de>
To: Joerg Roedel <joerg.roedel@amd.com>
Subject: Re: [PATCH 09/16] dma-debug: add checking for map/unmap_page/single
Date: Wed, 21 Jan 2009 01:17:32 +0100
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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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