mm: kmemcheck skip object if slab allocation failed

In the SLAB allocator kmemcheck_slab_alloc() is guarded against being
called in case the object is NULL.  In SLUB allocator this NULL pointer
invocation can happen, which seems like an oversight.

Move the NULL pointer check into kmemcheck code (kmemcheck_slab_alloc)
so the check gets moved out of the fastpath, when not compiled with
CONFIG_KMEMCHECK.

This is a step towards sharing post_alloc_hook between SLUB and SLAB,
because slab_post_alloc_hook() does not perform this check before
calling kmemcheck_slab_alloc().

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/kmemcheck.c

@@ -60,6 +60,9 @@ void kmemcheck_free_shadow(struct page *page, int order)
 void kmemcheck_slab_alloc(struct kmem_cache *s, gfp_t gfpflags, void *object,
 			  size_t size)
 {
+	if (unlikely(!object)) /* Skip object if allocation failed */
+		return;
+
 	/*
 	 * Has already been memset(), which initializes the shadow for us
 	 * as well.