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>

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 0cb0e12f87c741975b975df3bd856446b82fd465..112eda7c56bc816431a3031bfd8fb08e982299b4 100644 (file)
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2197,34 +2197,28 @@ 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)
-                                       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);
+                               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);
 
-                               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);
 

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index bee9776730fd76ae2ddf2d9650d8f55441d0d8c5..a9d256d6e909c1aecfc854732694d608256aeb15 100644 (file)
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -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);