Improve my last commit: use a separate condvar to serialize.

The advantage of using a separate condvar is that we can just use
cv_signal(9) instead of cv_broadcast(9). It makes no sense to wake up
multiple threads. It also makes the TTY code easier to understand.
t_dcdwait sounds totally unrelated.

1 files changed, 4 insertions, 2 deletions

diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index 4b2ce14..f98a70f 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -456,7 +456,7 @@ ttydev_write(struct cdev *dev, struct uio *uio, int ioflag)
 	} else {
 		/* Serialize write() calls. */
 		while (tp->t_flags & TF_BUSY_OUT) {
-			error = tty_wait(tp, &tp->t_dcdwait);
+			error = tty_wait(tp, &tp->t_outserwait);
 			if (error)
 				goto done;
 		}
@@ -464,7 +464,7 @@ ttydev_write(struct cdev *dev, struct uio *uio, int ioflag)
  		tp->t_flags |= TF_BUSY_OUT;
 		error = ttydisc_write(tp, uio, ioflag);
  		tp->t_flags &= ~TF_BUSY_OUT;
-		cv_broadcast(&tp->t_dcdwait);
+		cv_signal(&tp->t_outserwait);
 	}
 
 done:	tty_unlock(tp);
@@ -916,6 +916,7 @@ tty_alloc_mutex(struct ttydevsw *tsw, void *sc, struct mtx *mutex)
 
 	cv_init(&tp->t_inwait, "ttyin");
 	cv_init(&tp->t_outwait, "ttyout");
+	cv_init(&tp->t_outserwait, "ttyosr");
 	cv_init(&tp->t_bgwait, "ttybg");
 	cv_init(&tp->t_dcdwait, "ttydcd");
 
@@ -959,6 +960,7 @@ tty_dealloc(void *arg)
 	cv_destroy(&tp->t_outwait);
 	cv_destroy(&tp->t_bgwait);
 	cv_destroy(&tp->t_dcdwait);
+	cv_destroy(&tp->t_outserwait);
 
 	if (tp->t_mtx == &tp->t_mtxobj)
 		mtx_destroy(&tp->t_mtxobj);