[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, 2 insertions, 13 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index bd74e82d8a72..b846d87f2b56 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -784,11 +784,8 @@ restart:
         }
 
         clear_bit(TTY_LDISC, &tty->flags);
-        clear_bit(TTY_DONT_FLIP, &tty->flags);
-        if (o_tty) {
+        if (o_tty)
                 clear_bit(TTY_LDISC, &o_tty->flags);
-                clear_bit(TTY_DONT_FLIP, &o_tty->flags);
-        }
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 
         /*
@@ -1955,7 +1952,6 @@ static void release_dev(struct file * filp)
          * race with the set_ldisc code path.
          */
         clear_bit(TTY_LDISC, &tty->flags);
-        clear_bit(TTY_DONT_FLIP, &tty->flags);
         cancel_delayed_work(&tty->buf.work);
 
         /*
@@ -2784,13 +2780,6 @@ static void flush_to_ldisc(void *private_)
         if (disc == NULL)       /*  !TTY_LDISC */
                 return;
 
-        if (test_bit(TTY_DONT_FLIP, &tty->flags)) {
-                /*
-                 * Do it after the next timer tick:
-                 */
-                schedule_delayed_work(&tty->buf.work, 1);
-                goto out;
-        }
         spin_lock_irqsave(&tty->buf.lock, flags);
         while((tbuf = tty->buf.head) != NULL) {
                 while ((count = tbuf->commit - tbuf->read) != 0) {
@@ -2809,7 +2798,7 @@ static void flush_to_ldisc(void *private_)
                 tty_buffer_free(tty, tbuf);
         }
         spin_unlock_irqrestore(&tty->buf.lock, flags);
-out:
+
         tty_ldisc_deref(disc);
 }