static void get_futex_key_refs(union futex_key *key)
{
	if (!key->both.ptr)
		return;

	/*
	 * On MMU less systems futexes are always "private" as there is no per
	 * process address space. We need the smp wmb nevertheless - yes,
	 * arch/blackfin has MMU less SMP ...
	 */
	if (!IS_ENABLED(CONFIG_MMU)) {
		smp_mb(); /* explicit smp_mb(); (B) */
		return;
	}

	switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
	case FUT_OFF_INODE:
		ihold(key->shared.inode); /* implies smp_mb(); (B) */
		break;
	case FUT_OFF_MMSHARED:
		futex_get_mm(key); /* implies smp_mb(); (B) */
		break;
	default:
		/*
		 * Private futexes do not hold reference on an inode or
		 * mm, therefore the only purpose of calling get_futex_key_refs
		 * is because we need the barrier for the lockless waiter check.
		 */
		smp_mb(); /* explicit smp_mb(); (B) */
	}
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.