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Commit d8c1f929 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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tty: Only guarantee termios read safety for throttle/unthrottle 



No tty driver modifies termios during throttle() or unthrottle().
Therefore, only read safety is required.

However, tty_throttle_safe and tty_unthrottle_safe must still be
mutually exclusive; introduce throttle_mutex for that purpose.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fb7aa03d

drivers/tty/n_tty.c

+0 −4
Original line number Diff line number Diff line
@@ -1518,9 +1518,7 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp, 
		tty_set_flow_change(tty, TTY_THROTTLE_SAFE);

		if (receive_room(tty) >= TTY_THRESHOLD_THROTTLE)

			break;

		up_read(&tty->termios_rwsem);

		throttled = tty_throttle_safe(tty);

		down_read(&tty->termios_rwsem);

		if (!throttled)

			break;

	}
@@ -2086,9 +2084,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, 
			if (!tty->count)

				break;

			n_tty_set_room(tty);

			up_read(&tty->termios_rwsem);

			unthrottled = tty_unthrottle_safe(tty);

			down_read(&tty->termios_rwsem);

			if (!unthrottled)

				break;

		}

drivers/tty/tty_io.c

+1 −0
Original line number Diff line number Diff line
@@ -3015,6 +3015,7 @@ void initialize_tty_struct(struct tty_struct *tty, 
	tty->session = NULL;

	tty->pgrp = NULL;

	mutex_init(&tty->legacy_mutex);

	mutex_init(&tty->throttle_mutex);

	init_rwsem(&tty->termios_rwsem);

	init_ldsem(&tty->ldisc_sem);

	init_waitqueue_head(&tty->write_wait);

drivers/tty/tty_ioctl.c

+4 −4
Original line number Diff line number Diff line
@@ -151,7 +151,7 @@ int tty_throttle_safe(struct tty_struct *tty) 
{

	int ret = 0;



	down_write(&tty->termios_rwsem);

	mutex_lock(&tty->throttle_mutex);

	if (!test_bit(TTY_THROTTLED, &tty->flags)) {

		if (tty->flow_change != TTY_THROTTLE_SAFE)

			ret = 1;
@@ -161,7 +161,7 @@ int tty_throttle_safe(struct tty_struct *tty) 
				tty->ops->throttle(tty);

		}

	}

	up_write(&tty->termios_rwsem);

	mutex_unlock(&tty->throttle_mutex);



	return ret;

}
@@ -182,7 +182,7 @@ int tty_unthrottle_safe(struct tty_struct *tty) 
{

	int ret = 0;



	down_write(&tty->termios_rwsem);

	mutex_lock(&tty->throttle_mutex);

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

		if (tty->flow_change != TTY_UNTHROTTLE_SAFE)

			ret = 1;
@@ -192,7 +192,7 @@ int tty_unthrottle_safe(struct tty_struct *tty) 
				tty->ops->unthrottle(tty);

		}

	}

	up_write(&tty->termios_rwsem);

	mutex_unlock(&tty->throttle_mutex);



	return ret;

}

include/linux/tty.h

+1 −0
Original line number Diff line number Diff line
@@ -244,6 +244,7 @@ struct tty_struct { 


	struct mutex atomic_write_lock;

	struct mutex legacy_mutex;

	struct mutex throttle_mutex;

	struct rw_semaphore termios_rwsem;

	spinlock_t ctrl_lock;

	/* Termios values are protected by the termios rwsem */