SLUB's ksize() fails for size > 2048

I can't pass memory allocated by kmalloc() to ksize() if it is allocated by
SLUB allocator and size is larger than (I guess) PAGE_SIZE / 2.

The error of ksize() seems to be that it does not check if the allocation
was made by SLUB or the page allocator.
Reviewed-by: NPekka Enberg <penberg@cs.helsinki.fi>
Tested-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Christoph Lameter <clameter@sgi.com>, Matt Mackall <mpm@selenic.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -2558,8 +2558,12 @@ size_t ksize(const void *object)
 	if (unlikely(object == ZERO_SIZE_PTR))
 		return 0;
 
-	page = get_object_page(object);
+	page = virt_to_head_page(object);
 	BUG_ON(!page);
+
+	if (unlikely(!PageSlab(page)))
+		return PAGE_SIZE << compound_order(page);
+
 	s = page->slab;
 	BUG_ON(!s);