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().

---
 lib/is_single_threaded.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

index bd2bea9..391fd23 100644
@@ -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:

1.5.5.1

Wouldn't the old way be more efficient, given there's always going to be at least one thread? Granted, it's not much of an efficiency boost...

David

Yes, unfortunately. Before this change (in the likely case) we never do next_thread(), after this patch we always do list_first_entry().

Yes, and while_each_thread() is buggy. See the changelog in 0c740d0afc "introduce for_each_thread() to replace the buggy while_each_thread().

Yes, the race is almost purely theoretical, but still.

To clarify, we had some "real" bugs fixed by s/while_each_thread/ for_each_thread/, but only because while_each_thread() was used wrongly. for_each_thread() is more safe, it only needs the stable task_struct.

Oleg.

Fair enough.

David