From 4abc8e0a7335e2e79e3bb03eaed660ddc9c72bba Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Thu, 13 May 2021 04:35:06 +0300
Subject: [PATCH] ttydev_write: prevent stops while terminal is busied

PR:	255816

(cherry picked from commit 8cf912b017a04a2eec01fbaa1f7b9ef556403ede)
---
 sys/kern/tty.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index 00b4df67531..8700eb8f9ef 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -525,7 +525,7 @@ static int
 ttydev_write(struct cdev *dev, struct uio *uio, int ioflag)
 {
 	struct tty *tp = dev->si_drv1;
-	int error;
+	int defer, error;
 
 	error = ttydev_enter(tp);
 	if (error)
@@ -549,7 +549,9 @@ ttydev_write(struct cdev *dev, struct uio *uio, int ioflag)
 		}
 
 		tp->t_flags |= TF_BUSY_OUT;
+		defer = sigdeferstop(SIGDEFERSTOP_ERESTART);
 		error = ttydisc_write(tp, uio, ioflag);
+		sigallowstop(defer);
 		tp->t_flags &= ~TF_BUSY_OUT;
 		cv_signal(&tp->t_outserwait);
 	}