[PATCH] tty: Fix transient pty write() EIO

[Peter Hurley <peter@hurleysoftware.com>]

Commit 699390354da6c258b65bf8fa79cfd5feaede50b6
('pty: Ignore slave pty close() if never successfully opened')
introduced a bug with ptys whereby a write() in parallel with an
open() on an existing pty could mistakenly indicate an I/O error.

Only indicate an I/O error if the condition on open() actually exists.

Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
 drivers/tty/pty.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 9c2f1bc..dd08d3d 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -238,14 +238,9 @@ static void pty_flush_buffer(struct tty_struct *tty)
 
 static int pty_open(struct tty_struct *tty, struct file *filp)
 {
-	int	retval = -ENODEV;
-
 	if (!tty || !tty->link)
-		goto out;
-
-	set_bit(TTY_IO_ERROR, &tty->flags);
+		return -ENODEV;
 
-	retval = -EIO;
 	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 		goto out;
 	if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
@@ -256,9 +251,11 @@ static int pty_open(struct tty_struct *tty, struct file *filp)
 	clear_bit(TTY_IO_ERROR, &tty->flags);
 	clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 	set_bit(TTY_THROTTLED, &tty->flags);
-	retval = 0;
+	return 0;
+
 out:
-	return retval;
+	set_bit(TTY_IO_ERROR, &tty->flags);
+	return -EIO;
 }
 
 static void pty_set_termios(struct tty_struct *tty,
-- 
1.8.1.2