[src/trunk]: src/sys/kern When closing a tty, limit the amount of time spent ...

[gson <gson%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/d71ac3e2c964
branches:  trunk
changeset: 810132:d71ac3e2c964
user:      gson <gson%NetBSD.org@localhost>
date:      Wed Aug 19 12:02:55 2015 +0000

description:
When closing a tty, limit the amount of time spent waiting for the
output to drain to five seconds so that exiting processes with
buffered output for a serial port blocked by flow control or a pty
that is not being read do not hang indefinitely.  Should fix PRs
kern/12534 and kern/17171.  This is an updated version of the change
of tty.c 1.263.

diffstat:

 sys/kern/tty.c |  28 ++++++++++++++++++++--------
 1 files changed, 20 insertions(+), 8 deletions(-)

diffs (72 lines):

diff -r 56dd81cec113 -r d71ac3e2c964 sys/kern/tty.c
--- a/sys/kern/tty.c    Wed Aug 19 09:57:41 2015 +0000
+++ b/sys/kern/tty.c    Wed Aug 19 12:02:55 2015 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tty.c,v 1.264 2015/06/14 16:19:31 gson Exp $   */
+/*     $NetBSD: tty.c,v 1.265 2015/08/19 12:02:55 gson Exp $   */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -63,7 +63,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tty.c,v 1.264 2015/06/14 16:19:31 gson Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tty.c,v 1.265 2015/08/19 12:02:55 gson Exp $");
 
 #include "opt_compat_netbsd.h"
 
@@ -1536,10 +1536,10 @@
 }
 
 /*
- * Wait for output to drain.
+ * Wait for output to drain, or if this times out, flush it.
  */
-int
-ttywait(struct tty *tp)
+static int
+ttywait_timo(struct tty *tp, int timo)
 {
        int     error;
 
@@ -1549,9 +1549,11 @@
        while ((tp->t_outq.c_cc || ISSET(tp->t_state, TS_BUSY)) &&
            CONNECTED(tp) && tp->t_oproc) {
                (*tp->t_oproc)(tp);
-               error = ttysleep(tp, &tp->t_outcv, true, 0);
-               if (error)
+               error = ttysleep(tp, &tp->t_outcv, true, timo);
+               if (error == EWOULDBLOCK) {
+                       ttyflush(tp, FWRITE);
                        break;
+               }
        }
        mutex_spin_exit(&tty_lock);
 
@@ -1559,6 +1561,15 @@
 }
 
 /*
+ * Wait for output to drain.
+ */
+int
+ttywait(struct tty *tp)
+{
+       return ttywait_timo(tp, 0);
+}
+
+/*
  * Flush if successfully wait.
  */
 int
@@ -1566,7 +1577,8 @@
 {
        int     error;
 
-       if ((error = ttywait(tp)) == 0) {
+       error = ttywait_timo(tp, 5 * hz);
+       if (error == 0 || error == EWOULDBLOCK) {
                mutex_spin_enter(&tty_lock);
                ttyflush(tp, FREAD);
                mutex_spin_exit(&tty_lock);