Re: kern/12534 (Processes can hang at exit-time on ttyout)

[Andreas Gustafsson <gson%gson.org@localhost>]

The following reply was made to PR kern/12534; it has been noted by GNATS.

From: Andreas Gustafsson <gson%gson.org@localhost>
To: gnats-bugs%NetBSD.org@localhost, Antti Kantee <pooka%iki.fi@localhost>
Cc: 
Subject: Re: kern/12534 (Processes can hang at exit-time on ttyout)
Date: Fri, 12 Jun 2015 15:49:54 +0300

 Hi,
 
 My system that was suffering from symptoms similar to kern/12534
 has now been running with the following patch for more than nine
 months, and it seems to have fixed the problem and not caused any new
 ones.  OK to commit?
 
 Index: src/sys/kern/tty.c
 ===================================================================
 RCS file: /bracket/repo/src/sys/kern/tty.c,v
 retrieving revision 1.249.8.2
 diff -u -r1.249.8.2 tty.c
 --- src/sys/kern/tty.c	20 Aug 2012 19:15:36 -0000	1.249.8.2
 +++ src/sys/kern/tty.c	30 Aug 2014 13:51:17 -0000
 @@ -1525,10 +1525,10 @@
  }
  
  /*
 - * Wait for output to drain.
 + * Wait for output to drain, or if this times out, flush it.
   */
  int
 -ttywait(struct tty *tp)
 +ttywait_timo(struct tty *tp, int timo)
  {
  	int	error;
  
 @@ -1538,9 +1538,11 @@
  	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) {
 +			ttyflush(tp, FWRITE);
  			break;
 +		}
  	}
  	mutex_spin_exit(&tty_lock);
  
 @@ -1548,6 +1550,15 @@
  }
  
  /*
 + * Wait for output to drain.
 + */
 +int
 +ttywait(struct tty *tp)
 +{
 +	return ttywait_timo(tp, 0);
 +}
 +
 +/*
   * Flush if successfully wait.
   */
  int
 @@ -1555,7 +1566,8 @@
  {
  	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);
 Index: src/sys/sys/tty.h
 ===================================================================
 RCS file: /bracket/repo/src/sys/sys/tty.h,v
 retrieving revision 1.90
 diff -u -r1.90 tty.h
 --- src/sys/sys/tty.h	24 Sep 2011 00:05:38 -0000	1.90
 +++ src/sys/sys/tty.h	30 Aug 2014 13:51:17 -0000
 @@ -286,6 +286,7 @@
  int	 ttysleep(struct tty *, kcondvar_t *, bool, int);
  int	 ttypause(struct tty *, int);
  int	 ttywait(struct tty *);
 +int	 ttywait_timo(struct tty *, int timo);
  int	 ttywflush(struct tty *);
  void	 ttysig(struct tty *, enum ttysigtype, int);
  void	 tty_attach(struct tty *);
 
 -- 
 Andreas Gustafsson, gson%gson.org@localhost