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Message-ID: <20090727115723.1e8de60e@lxorguk.ukuu.org.uk>
Date: Mon, 27 Jul 2009 11:57:23 +0100
From: Alan Cox <alan@...rguk.ukuu.org.uk>
To: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
"Rafael J. Wysocki" <rjw@...k.pl>, Ray Lee <ray-lk@...rabbit.org>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Regression] kdesu broken
> I see. It sounds like good thing. The attached patch or something?
> Anyway, I'm not familiar with the tty stuff obviously, so, I'm not sure
> whether this patch is right or not.
It turns out to be a little bit trickier than I thought because of open
v close v flush_to_ldisc races (some of the open/close ones being long
standing).
We now use tty->buf.lock to keep EOF/EOFPENDING/OTHER_CLOSED all in order
together. That has no real cost as we already hold the buf.lock in the hot
path which is flush_to_ldisc.
Anyway this is my current thoughts (not yet given a testing)
diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
index ff47907..acae995 100644
--- a/drivers/char/n_tty.c
+++ b/drivers/char/n_tty.c
@@ -1777,7 +1777,8 @@ do_it_again:
tty->minimum_to_wake = (minimum - (b - buf));
if (!input_available_p(tty, 0)) {
- if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
+ if (test_bit(TTY_EOF, &tty->flags)) {
+ /* PTY pair closed and all data consumed */
retval = -EIO;
break;
}
diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 6e6942c..de10cc0 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -38,6 +38,9 @@ static struct tty_driver *pts_driver;
static void pty_close(struct tty_struct *tty, struct file *filp)
{
+ struct tty_struct *pair;
+ unsigned long flags;
+
BUG_ON(!tty);
if (tty->driver->subtype == PTY_TYPE_MASTER)
WARN_ON(tty->count > 1);
@@ -47,13 +50,22 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
}
wake_up_interruptible(&tty->read_wait);
wake_up_interruptible(&tty->write_wait);
+
tty->packet = 0;
- if (!tty->link)
+ pair = tty->link;
+ if (!pair)
return;
- tty->link->packet = 0;
- set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
- wake_up_interruptible(&tty->link->read_wait);
- wake_up_interruptible(&tty->link->write_wait);
+
+ spin_lock_irqsave(&pair->buf.lock, flags);
+ pair->packet = 0;
+ /* Indicate that the other end is now closed, set the
+ ENDPENDING marker so that the true end can be processed by
+ the line discipline */
+ set_bit(TTY_EOFPENDING, &pair->flags);
+ set_bit(TTY_OTHER_CLOSED, &pair->flags);
+ spin_unlock_irqrestore(&pair->buf.lock, flags);
+ wake_up_interruptible(&pair->read_wait);
+ wake_up_interruptible(&pair->write_wait);
if (tty->driver->subtype == PTY_TYPE_MASTER) {
set_bit(TTY_OTHER_CLOSED, &tty->flags);
#ifdef CONFIG_UNIX98_PTYS
@@ -180,7 +192,6 @@ static void pty_flush_buffer(struct tty_struct *tty)
if (!to)
return;
- /* tty_buffer_flush(to); FIXME */
if (to->packet) {
spin_lock_irqsave(&tty->ctrl_lock, flags);
tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
@@ -191,23 +202,30 @@ static void pty_flush_buffer(struct tty_struct *tty)
static int pty_open(struct tty_struct *tty, struct file *filp)
{
- int retval = -ENODEV;
+ int retval = -EIO;
+ unsigned long flags;
+ struct tty_struct *pair;
- if (!tty || !tty->link)
- goto out;
+ if (tty == NULL || (pair = tty->link) == NULL)
+ return -ENODEV;
- retval = -EIO;
if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
+ return -EIO;
+ spin_lock_irqsave(&pair->buf.lock, flags);
+ if (test_bit(TTY_PTY_LOCK, &pair->flags))
goto out;
- if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
- goto out;
- if (tty->link->count != 1)
+ if (pair->count != 1)
goto out;
- clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
+ clear_bit(TTY_OTHER_CLOSED, &pair->flags);
+ /* The buf.lock stops this racing a flush_to_ldisc from
+ the other end */
+ clear_bit(TTY_EOFPENDING, &pair->flags);
+ clear_bit(TTY_EOF, &pair->flags);
set_bit(TTY_THROTTLED, &tty->flags);
retval = 0;
out:
+ spin_unlock_irqrestore(&pair->buf.lock, flags);
return retval;
}
diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
index 810ee25..448cd1d 100644
--- a/drivers/char/tty_buffer.c
+++ b/drivers/char/tty_buffer.c
@@ -119,6 +119,12 @@ static void __tty_buffer_flush(struct tty_struct *tty)
tty_buffer_free(tty, thead);
}
tty->buf.tail = NULL;
+ /* We can EOF a pty/tty pair with a flush as well as by consuming
+ all the data left over */
+ if (test_bit(TTY_EOFPENDING, &tty->flags)) {
+ set_bit(TTY_EOF, &tty->flags);
+ wake_up(&tty->read_wait);
+ }
}
/**
@@ -455,6 +461,10 @@ static void flush_to_ldisc(struct work_struct *work)
clear_bit(TTY_FLUSHPENDING, &tty->flags);
wake_up(&tty->read_wait);
}
+ if (tty->buf.head == NULL && test_bit(TTY_EOFPENDING, &tty->flags)) {
+ wake_up(&tty->read_wait);
+ set_bit(TTY_EOF, &tty->flags);
+ }
clear_bit(TTY_FLUSHING, &tty->flags);
spin_unlock_irqrestore(&tty->buf.lock, flags);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 85aa525..427d107 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -321,6 +321,8 @@ struct tty_struct {
#define TTY_LDISC 9 /* Line discipline attached */
#define TTY_LDISC_CHANGING 10 /* Line discipline changing */
#define TTY_LDISC_OPEN 11 /* Line discipline is open */
+#define TTY_EOF 12 /* TTY/PTY pair at EOF */
+#define TTY_EOFPENDING 13 /* TTY/PTY pair EOF when data emptied */
#define TTY_HW_COOK_OUT 14 /* Hardware can do output cooking */
#define TTY_HW_COOK_IN 15 /* Hardware can do input cooking */
#define TTY_PTY_LOCK 16 /* pty private */
--
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