Add VM_BUG_ON in case someone uses page_mapping on a slab page
Christoph Lameter [Tue, 17 Jul 2007 11:03:33 +0000 (04:03 -0700)]
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 slab object may not be properly aligned.  The page
oriented functions of the VM expect to operate on page aligned, page sized
objects.  Operations on object 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 <clameter@sgi.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

index 4c482a3..a5c4518 100644 (file)
@@ -599,6 +599,7 @@ static inline struct address_space *page_mapping(struct page *page)
 {
        struct address_space *mapping = page->mapping;
 
+       VM_BUG_ON(PageSlab(page));
        if (unlikely(PageSwapCache(page)))
                mapping = &swapper_space;
 #ifdef CONFIG_SLUB