page_mapping must avoid slub pages

Nicolas Ferre reports oops from flush_dcache_page() on ARM when using
SLUB: which reuses page->mapping as page->slab. The page_mapping()
function, used by ARM and PA-RISC flush_dcache_page() implementations,
must not confuse SLUB pages with those which have page->mapping set.

Signed-off-by: Hugh Dickins <[e-mail]>
Cc: Nicolas Ferre <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/mm.h

···
 
 	if (unlikely(PageSwapCache(page)))
 		mapping = &swapper_space;
+#ifdef CONFIG_SLUB
+	else if (unlikely(PageSlab(page)))
+		mapping = NULL;
+#endif
 	else if (unlikely((unsigned long)mapping & PAGE_MAPPING_ANON))
 		mapping = NULL;
 	return mapping;