Messages in this thread Patch in this message | | | Date | Fri, 10 Jul 2009 22:34:04 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] dma-debug: Fix the overlap() function to be correct and readable |
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > > On Fri, 10 Jul 2009, Ingo Molnar wrote: > > > > How about the patch below? Lightly tested. > > > > if (!PageHighMem(page)) { > > - void *addr = ((char *)page_address(page)) + offset; > > + void *addr = (void *)page_address(page) + offset; > > + > > Why is that 'void *' cast there? page_address() is already a void *. > > Other than that it obviously looks good to me. But I never see my > own bugs.
hm, indeed. I distinctly remember page_address() having been unsigned long ten years ago.
And yes, i still have a "highmem-2.2.21-A0" patch proving it:
--- linux/include/linux/pagemap.h.orig Thu Oct 7 14:54:24 1999 +++ linux/include/linux/pagemap.h Wed Oct 13 02:44:03 1999 @@ -11,12 +11,24 @@ #include <linux/mm.h> #include <linux/fs.h> +#include <linux/list.h> -static inline unsigned long page_address(struct page * page) +extern inline unsigned long FIXME_page_address(struct page * page) { + if (PageHIGHMEM(page)) + BUG(); return PAGE_OFFSET + ((page - mem_map) << PAGE_SHIFT);
Which, beyond being a rather embarrasing hunk (whose author i wont name voluntarily - i'll rather take the 5th), also shows that page_address() started out as an unsigned long.
Which got cleaned up for good once we added page->address, instead of the above direct calculation.
( Note to self: consider checking the types of core MM facilities somewhat more frequently than every 10 years. )
Ingo
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