kasan: fix a2 allocation and remove explicit cast in atomic tests

Address the additional feedback since 4e76c8c kasan: add atomic tests
(""kasan: add atomic tests") by removing an explicit cast and fixing the
size as well as the check of the allocation of `a2`.

Link: https://lkml.kernel.org/r/20240224105414.211995-1-paul.heidekrueger@tum.de
Link: https://lore.kernel.org/all/20240131210041.686657-1-paul.heidekrueger@tum.de/T/#u
Fixes: 4e76c8c ("kasan: add atomic tests")
Signed-off-by: Paul Heidekrüger <paul.heidekrueger@tum.de>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=214055
Reviewed-by: Marco Elver <elver@google.com>
Tested-by: Marco Elver <elver@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/kasan/kasan_test.c

@@ -700,7 +700,7 @@ static void kmalloc_uaf3(struct kunit *test)
 
 static void kasan_atomics_helper(struct kunit *test, void *unsafe, void *safe)
 {
-	int *i_unsafe = (int *)unsafe;
+	int *i_unsafe = unsafe;
 
 	KUNIT_EXPECT_KASAN_FAIL(test, READ_ONCE(*i_unsafe));
 	KUNIT_EXPECT_KASAN_FAIL(test, WRITE_ONCE(*i_unsafe, 42));
@@ -766,8 +766,8 @@ static void kasan_atomics(struct kunit *test)
 	 */
 	a1 = kzalloc(48, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, a1);
-	a2 = kzalloc(sizeof(int), GFP_KERNEL);
-	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, a1);
+	a2 = kzalloc(sizeof(atomic_long_t), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, a2);
 
 	/* Use atomics to access the redzone. */
 	kasan_atomics_helper(test, a1 + 48, a2);