mempool: skip slub_debug poisoning when KASAN is enabled

With the changes in the following patch, KASAN starts saving its metadata
within freed mempool elements.

Thus, skip slub_debug poisoning and checking of mempool elements when
KASAN is enabled.  Corruptions of freed mempool elements will be detected
by KASAN anyway.

Link: https://lkml.kernel.org/r/98a4b1617e8ceeb266ef9a46f5e8c7f67a563ad2.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>

Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mempool.c

@@ -56,6 +56,10 @@ static void __check_element(mempool_t *pool, void *element, size_t size)
 
 static void check_element(mempool_t *pool, void *element)
 {
+	/* Skip checking: KASAN might save its metadata in the element. */
+	if (kasan_enabled())
+		return;
+
 	/* Mempools backed by slab allocator */
 	if (pool->free == mempool_kfree) {
 		__check_element(pool, element, (size_t)pool->pool_data);
@@ -81,6 +85,10 @@ static void __poison_element(void *element, size_t size)
 
 static void poison_element(mempool_t *pool, void *element)
 {
+	/* Skip poisoning: KASAN might save its metadata in the element. */
+	if (kasan_enabled())
+		return;
+
 	/* Mempools backed by slab allocator */
 	if (pool->alloc == mempool_kmalloc) {
 		__poison_element(element, (size_t)pool->pool_data);