s390: get_user_pages_fast() might sleep

Let's annotate it correctly, so we directly get a warning if
we ever were to use it in atomic/preempt_disable/spinlock environment.
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/gup.c

@@ -233,6 +233,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	struct mm_struct *mm = current->mm;
 	int nr, ret;
 
+	might_sleep();
 	start &= PAGE_MASK;
 	nr = __get_user_pages_fast(start, nr_pages, write, pages);
 	if (nr == nr_pages)