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    SubjectRe: [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 :)


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