Commit 52bce7f8 authored Nov 05, 2014 by Peter Hurley Committed by Greg Kroah-Hartman Nov 05, 2014

pty, n_tty: Simplify input processing on final close



When releasing one end of a pty pair, that end may just have written
to the other, which the input processing worker, flush_to_ldisc(), is
still working on but has not completed the copy to the other end's
read buffer. So input may not appear to be available to a waiting
reader but yet TTY_OTHER_CLOSED is now observed. The n_tty line
discipline has worked around this by waiting for input processing
to complete and then re-checking if input is available before
exiting with -EIO.

Since the tty/ldisc lock reordering, the wait for input processing
to complete can now occur during final close before setting
TTY_OTHER_CLOSED. In this way, a waiting reader is guaranteed to
see input available (if any) before observing TTY_OTHER_CLOSED.

Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 1bb95415

drivers/tty/n_tty.c

+20 −26

Original line number	Diff line number	Diff line
		@@ -2197,14 +2197,9 @@ 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)) {
		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)
		@@ -2225,7 +2220,6 @@ static ssize_t n_tty_read(struct tty_struct tty, struct file file,
		down_read(&tty->termios_rwsem);
		continue;
		}
		}
		__set_current_state(TASK_RUNNING);

		if (ldata->icanon && !L_EXTPROC(tty)) {

drivers/tty/pty.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -53,6 +53,7 @@ static void pty_close(struct tty_struct tty, struct file filp)
		/* Review - krefs on tty_link ?? */
		if (!tty->link)
		return;
		tty_flush_to_ldisc(tty->link);
		set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
		wake_up_interruptible(&tty->link->read_wait);
		wake_up_interruptible(&tty->link->write_wait);

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