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Fix draining in ttydev_leave():

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1.  ERESTART is not only returned when the revoke count changed. It
    is also returned when a signal is received. While a change in
    the revoke count should be ignored, a signal should not.
2.  Waiting until the output queue is entirely drained can cause a
    hang when the underlying device is stuck or broken.

Have tty_drain() take care of this by telling it when we're leaving.
When leaving, tty_drain() will use a timed wait to address point 2
above and it will check the revoke count to handle point 1 above.
The timeout is set to 1 second, which is arbitrary and long enough
to expect a change in the output queue.

Discussed with: jilles@
Reported by: Yamagi Burmeister <lists@yamagi.org>
This commit is contained in:
Marcel Moolenaar 2014-10-09 02:30:38 +00:00
parent cdfd89cea1
commit 383f423be1
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=272789
1 changed files with 25 additions and 10 deletions
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35
sys/kern/tty.c
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@ -123,9 +123,10 @@ tty_watermarks(struct tty *tp)
}
static int
tty_drain(struct tty *tp)
tty_drain(struct tty *tp, int leaving)
{
int error;
size_t bytesused;
int error, revokecnt;
if (ttyhook_hashook(tp, getc_inject))
/* buffer is inaccessible */
@ -134,11 +135,27 @@ tty_drain(struct tty *tp)
while (ttyoutq_bytesused(&tp->t_outq) > 0) {
ttydevsw_outwakeup(tp);
/* Could be handled synchronously. */
if (ttyoutq_bytesused(&tp->t_outq) == 0)
bytesused = ttyoutq_bytesused(&tp->t_outq);
if (bytesused == 0)
return (0);
/* Wait for data to be drained. */
error = tty_wait(tp, &tp->t_outwait);
if (leaving) {
revokecnt = tp->t_revokecnt;
error = tty_timedwait(tp, &tp->t_outwait, hz);
switch (error) {
case ERESTART:
if (revokecnt != tp->t_revokecnt)
error = 0;
break;
case EWOULDBLOCK:
if (ttyoutq_bytesused(&tp->t_outq) < bytesused)
error = 0;
break;
}
} else
error = tty_wait(tp, &tp->t_outwait);
if (error)
return (error);
}
@ -191,10 +208,8 @@ ttydev_leave(struct tty *tp)
/* Drain any output. */
MPASS((tp->t_flags & TF_STOPPED) == 0);
if (!tty_gone(tp)) {
while (tty_drain(tp) == ERESTART)
;
}
if (!tty_gone(tp))
tty_drain(tp, 1);
ttydisc_close(tp);
@ -1528,7 +1543,7 @@ tty_generic_ioctl(struct tty *tp, u_long cmd, void *data, int fflag,
/* Set terminal flags through tcsetattr(). */
if (cmd == TIOCSETAW || cmd == TIOCSETAF) {
error = tty_drain(tp);
error = tty_drain(tp, 0);
if (error)
return (error);
if (cmd == TIOCSETAF)
@ -1707,7 +1722,7 @@ tty_generic_ioctl(struct tty *tp, u_long cmd, void *data, int fflag,
}
case TIOCDRAIN:
/* Drain TTY output. */
return tty_drain(tp);
return tty_drain(tp, 0);
case TIOCCONS:
/* Set terminal as console TTY. */
if (*(int *)data) {