[PATCH] remove TTY_DONT_FLIP

Remove TTY_DONT_FLIP tty flag.  This flag was introduced in 2.1.X kernels
to prevent the N_TTY line discipline functions read_chan() and
n_tty_receive_buf() from running at the same time.  2.2.15 introduced
tty->read_lock to protect access to the N_TTY read buffer, which is the
only state requiring protection between these two functions.

The current TTY_DONT_FLIP implementation is broken for SMP, and is not
universally honored by drivers that send data directly to the line
discipline receive_buf function.

Because TTY_DONT_FLIP is not necessary, is broken in implementation, and is
not universally honored, it is removed.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 5 deletions

diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
index b9371d5bf790..603b9ade5eb0 100644
--- a/drivers/char/n_tty.c
+++ b/drivers/char/n_tty.c
@@ -1132,7 +1132,7 @@ static inline int input_available_p(struct tty_struct *tty, int amt)
  *      buffer, and once to drain the space from the (physical) beginning of
  *      the buffer to head pointer.
  *
- *      Called under the tty->atomic_read_lock sem and with TTY_DONT_FLIP set
+ *      Called under the tty->atomic_read_lock sem
  *
  */
  
@@ -1271,7 +1271,6 @@ do_it_again:
         }
 
         add_wait_queue(&tty->read_wait, &wait);
-        set_bit(TTY_DONT_FLIP, &tty->flags);
         while (nr) {
                 /* First test for status change. */
                 if (tty->packet && tty->link->ctrl_status) {
@@ -1315,9 +1314,7 @@ do_it_again:
                                 break;
                         }
                         n_tty_set_room(tty);
-                        clear_bit(TTY_DONT_FLIP, &tty->flags);
                         timeout = schedule_timeout(timeout);
-                        set_bit(TTY_DONT_FLIP, &tty->flags);
                         continue;
                 }
                 __set_current_state(TASK_RUNNING);
@@ -1394,7 +1391,6 @@ do_it_again:
                 if (time)
                         timeout = time;
         }
-        clear_bit(TTY_DONT_FLIP, &tty->flags);
         mutex_unlock(&tty->atomic_read_lock);
         remove_wait_queue(&tty->read_wait, &wait);