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Commit 817d6d3b authored by Paul Fulghum's avatar Paul Fulghum Committed by Linus Torvalds
Browse files

[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: default avatarPaul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e0ac4761

drivers/char/mxser.c

+0 −1
Original line number Diff line number Diff line
@@ -996,7 +996,6 @@ static int mxser_open(struct tty_struct *tty, struct file *filp) 


	info->session = current->signal->session;

	info->pgrp = process_group(current);

	clear_bit(TTY_DONT_FLIP, &tty->flags);



	/*

	status = mxser_get_msr(info->base, 0, info->port);

drivers/char/n_tty.c

+1 −5
Original line number Diff line number Diff line
@@ -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 @@ static ssize_t read_chan(struct tty_struct *tty, struct file *file, 
	}



	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 @@ static ssize_t read_chan(struct tty_struct *tty, struct file *file, 
				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 @@ static ssize_t read_chan(struct tty_struct *tty, struct file *file, 
		if (time)

			timeout = time;

	}

	clear_bit(TTY_DONT_FLIP, &tty->flags);

	mutex_unlock(&tty->atomic_read_lock);

	remove_wait_queue(&tty->read_wait, &wait);

drivers/char/pty.c

+1 −1
Original line number Diff line number Diff line
@@ -101,7 +101,7 @@ static void pty_unthrottle(struct tty_struct * tty) 
 *

 * FIXME: Our pty_write method is called with our ldisc lock held but

 * not our partners. We can't just take the other one blindly without

 * risking deadlocks.  There is also the small matter of TTY_DONT_FLIP

 * risking deadlocks.

 */

static int pty_write(struct tty_struct * tty, const unsigned char *buf, int count)

{

drivers/char/tty_io.c

+2 −13
Original line number Diff line number Diff line
@@ -784,11 +784,8 @@ static int tty_set_ldisc(struct tty_struct *tty, int ldisc) 
	}



	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);

}

drivers/serial/crisv10.c

+0 −6
Original line number Diff line number Diff line
@@ -2573,12 +2573,6 @@ static void flush_to_flip_buffer(struct e100_serial *info) 


	DFLIP(

	  if (1) {



		  if (test_bit(TTY_DONT_FLIP, &tty->flags)) {

			  DEBUG_LOG(info->line, "*** TTY_DONT_FLIP set flip.count %i ***\n", tty->flip.count);

			  DEBUG_LOG(info->line, "*** recv_cnt %i\n", info->recv_cnt);

		  } else {

		  }

		  DEBUG_LOG(info->line, "*** rxtot %i\n", info->icount.rx);

		  DEBUG_LOG(info->line, "ldisc %lu\n", tty->ldisc.chars_in_buffer(tty));

		  DEBUG_LOG(info->line, "room  %lu\n", tty->ldisc.receive_room(tty));