lib/is_single_threaded.c: change current_is_single_threaded() to use for_each_thread()

Change current_is_single_threaded() to use for_each_thread() rather than
deprecated while_each_thread().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/is_single_threaded.c

@@ -36,8 +36,7 @@ bool current_is_single_threaded(void)
 		if (unlikely(p == task->group_leader))
 			continue;
 
-		t = p;
-		do {
+		for_each_thread(p, t) {
 			if (unlikely(t->mm == mm))
 				goto found;
 			if (likely(t->mm))
@@ -48,7 +47,7 @@ bool current_is_single_threaded(void)
 			 * forked before exiting.
 			 */
 			smp_rmb();
-		} while_each_thread(p, t);
+		}
 	}
 	ret = true;
 found: