fix potential race condition in detached threads

after the thread unmaps its own stack/thread structure, the kernel,
performing child tid clear and futex wake, could clobber a new mapping
made at the same location as the just-removed thread's tid field.
disable kernel clearing of child tid to prevent this.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/thread/pthread_detach.c b/src/thread/pthread_detach.c
index 8ef03d51..e8032398 100644
--- a/src/thread/pthread_detach.c
+++ b/src/thread/pthread_detach.c
@@ -5,7 +5,7 @@ int pthread_detach(pthread_t t)
 	/* Cannot detach a thread that's already exiting */
 	if (a_swap(&t->exitlock, 1))
 		return pthread_join(t, 0);
-	t->detached = 1;
-	t->exitlock = 0;
+	t->detached = 2;
+	a_store(&t->exitlock, 0);
 	return 0;
 }