On Fri, 22 Jun 2007, Christoph Lameter wrote:
>
> Add VM_BUG_ON in case someone uses page_mapping on a slab page
>
> Detect slab objects being passed to the page oriented functions of the VM.
>
> It is not sufficient to simply return NULL because the functions calling
> page_mapping may depend on other items of the page_struct also to be setup
> properly. Moreover the slab object may not be properly aligned. The page
> orientedfunctions of the VM expect to operate on page aligned, page sized
> objects. operations on objects straddling page boundaries may only affect
> the objects partially which may lead to surprising results.
>
> It is better to detect eventually remaining uses and eliminate them.
>
> Signed-off-by: Christoph Lameter <[email protected]>
I'm quite happy with this approach for 2.6.23-rc, along with your ARM
dma_map patch which (if I understood aright) rmk approved. Except,
haven't you misplaced that VM_BUG_ON between an if and its else?
And I'd much prefer you to make it an outright BUG_ON, because
many testers have those VM_BUG_ONs configured out.
Hugh
>
> ---
> include/linux/mm.h | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> Index: linux-2.6/include/linux/mm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm.h 2007-06-22 10:33:27.000000000 -0700
> +++ linux-2.6/include/linux/mm.h 2007-06-22 10:34:09.000000000 -0700
> @@ -603,10 +603,7 @@ static inline struct address_space *page
>
> if (unlikely(PageSwapCache(page)))
> mapping = &swapper_space;
> -#ifdef CONFIG_SLUB
> - else if (unlikely(PageSlab(page)))
> - mapping = NULL;
> -#endif
> + VM_BUG_ON(PageSlab(page));
> else if (unlikely((unsigned long)mapping & PAGE_MAPPING_ANON))
> mapping = NULL;
> return mapping;
>
-
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