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

[christos%zoulas.com@localhost (Christos Zoulas)]

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

From: christos%zoulas.com@localhost (Christos Zoulas)
To: gnats-bugs%NetBSD.org@localhost, kern-bug-people%netbsd.org@localhost, 
	gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost, pooka%iki.fi@localhost
Cc: gson%gson.org@localhost
Subject: Re: kern/12534 (Processes can hang at exit-time on ttyout)
Date: Fri, 12 Jun 2015 10:35:19 -0400

 On Jun 12, 12:55pm, gson%gson.org@localhost (Andreas Gustafsson) wrote:
 -- Subject: Re: kern/12534 (Processes can hang at exit-time on ttyout)
 
 |  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?
 
 Well, no need to expose ttywait_timeo() since it is only used internally
 (it should be static). Your fix changes the behavior of ttywflush() which
 looks fine for now (since only if_sl.c and if_strip.c use it directly and
 in that case it does not matter since they call it on close. I would add
 a comment though to to ttywflush since it does not really wait anymore forever
 as it used to do, and if one wants to really wait for it to complete, they
 need to check for EWOULDBLOCK and put it in a loop. Nobody even checks
 for the return for ttywflush() now so perhaps even adding the comment is
 excessive :-)
 
 I think you should commit it (with the static)
 
 christos
 
 |  
 |  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
 |  
 -- End of excerpt from Andreas Gustafsson