kasan: open-code kasan_unpoison_slab

There's the external annotation kasan_unpoison_slab() that is currently
defined as static inline and uses kasan_unpoison_range(). Open-code this
function in mempool.c. Otherwise with an upcoming change this function
will result in an unnecessary function call.

Link: https://lkml.kernel.org/r/131a6694a978a9a8b150187e539eecc8bcbf759b.1606162397.git.andreyknvl@google.com
Link: https://linux-review.googlesource.com/id/Ia7c8b659f79209935cbaab3913bf7f082cc43a0eSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kasan.h

@@ -107,11 +107,6 @@ struct kasan_cache {
 	int free_meta_offset;
 };
 
-size_t __ksize(const void *);
-static inline void kasan_unpoison_slab(const void *ptr)
-{
-	kasan_unpoison_range(ptr, __ksize(ptr));
-}
 size_t kasan_metadata_size(struct kmem_cache *cache);
 
 bool kasan_save_enable_multi_shot(void);
@@ -167,7 +162,6 @@ static inline bool kasan_slab_free(struct kmem_cache *s, void *object,
 	return false;
 }
 
-static inline void kasan_unpoison_slab(const void *ptr) { }
 static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
 
 #endif /* CONFIG_KASAN */

mm/mempool.c

@@ -112,7 +112,7 @@ static __always_inline void kasan_poison_element(mempool_t *pool, void *element)
 static void kasan_unpoison_element(mempool_t *pool, void *element)
 {
 	if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc)
-		kasan_unpoison_slab(element);
+		kasan_unpoison_range(element, __ksize(element));
 	else if (pool->alloc == mempool_alloc_pages)
 		kasan_alloc_pages(element, (unsigned long)pool->pool_data);
 }