From 2524cc787e0f817025d6f6041305c16faf72a660 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Fri, 27 Sep 2013 13:27:05 -0400 Subject: [PATCH] tty: Fix pty master read() after slave closes Commit 7a354a5f2bdfb768a963bb2376b7a1725ae0fec1, 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 Signed-off-by: Peter Hurley Tested-by: Mikael Pettersson Signed-off-by: Greg Kroah-Hartman --- 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); -- 2.39.5