kasan: clean up setting free info in kasan_slab_free

Put kasan_stack_collection_enabled() check and kasan_set_free_info() calls
next to each other.

The way this was previously implemented was a minor optimization that
relied of the the fact that kasan_stack_collection_enabled() is always
true for generic KASAN.  The confusion that this brings outweights saving
a few instructions.

Link: https://lkml.kernel.org/r/f838e249be5ab5810bf54a36ef5072cfd80e2da7.1612546384.git.andreyknvl@google.comSigned-off-by: NAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: NMarco Elver <elver@google.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: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/kasan/common.c

@@ -350,13 +350,11 @@ static bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
 
 	kasan_poison(object, cache->object_size, KASAN_KMALLOC_FREE);
 
-	if (!kasan_stack_collection_enabled())
-		return false;
-
 	if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine))
 		return false;
 
-	kasan_set_free_info(cache, object, tag);
+	if (kasan_stack_collection_enabled())
+		kasan_set_free_info(cache, object, tag);
 
 	return kasan_quarantine_put(cache, object);
 }