From f8747d4a466ab2cafe56112c51b3379f9fdb7a12 Mon Sep 17 00:00:00 2001
From: Peter Hurley <peter@hurleysoftware.com>
Date: Fri, 27 Sep 2013 13:27:05 -0400
Subject: [PATCH] tty: Fix pty master read() after slave closes
Commit f95499c3030fe1bfad57745f2db1959c5b43dca8,
n_tty: Don't wait for buffer work in read() loop
creates a race window which can cause a pty master read()
to miss the last pty slave write(s) and return -EIO instead,
thus signalling the pty slave is closed. This can happen when
the pty slave is written and immediately closed but before the
tty buffer i/o loop receives the new input; the pty master
read() is scheduled, sees its read buffer is empty and the
pty slave has been closed, and exits.
Because tty_flush_to_ldisc() has significant performance impact
for parallel i/o, rather than revert the commit, special case this
condition (ie., when the read buffer is empty and the 'other' pty
has been closed) and, only then, wait for buffer work to complete
before re-testing if the read buffer is still empty.
As before, subsequent pty master reads return any available data
until no more data is available, and then returns -EIO to
indicate the pty slave has closed.
Reported-by: Mikael Pettersson <mikpelinux@gmail.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Tested-by: Mikael Pettersson <mikpelinux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tty/n_tty.c | 46 +++++++++++++++++++++++++--------------------
1 file changed, 26 insertions(+), 20 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 01bf5eb4f2384..7a744b69c3d14 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2183,28 +2183,34 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
if (!input_available_p(tty, 0)) {
if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
- retval = -EIO;
- break;
- }
- if (tty_hung_up_p(file))
- break;
- if (!timeout)
- break;
- if (file->f_flags & O_NONBLOCK) {
- retval = -EAGAIN;
- break;
- }
- if (signal_pending(current)) {
- retval = -ERESTARTSYS;
- break;
- }
- n_tty_set_room(tty);
- up_read(&tty->termios_rwsem);
+ up_read(&tty->termios_rwsem);
+ tty_flush_to_ldisc(tty);
+ down_read(&tty->termios_rwsem);
+ if (!input_available_p(tty, 0)) {
+ retval = -EIO;
+ break;
+ }
+ } else {
+ if (tty_hung_up_p(file))
+ break;
+ if (!timeout)
+ break;
+ if (file->f_flags & O_NONBLOCK) {
+ retval = -EAGAIN;
+ break;
+ }
+ if (signal_pending(current)) {
+ retval = -ERESTARTSYS;
+ break;
+ }
+ n_tty_set_room(tty);
+ up_read(&tty->termios_rwsem);
- timeout = schedule_timeout(timeout);
+ timeout = schedule_timeout(timeout);
- down_read(&tty->termios_rwsem);
- continue;
+ down_read(&tty->termios_rwsem);
+ continue;
+ }
}
__set_current_state(TASK_RUNNING);
--
2.30.2