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tty: Only guarantee termios read safety for throttle/unthrottle

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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: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2013-06-15 09:14:31 -04:00 committed by Greg Kroah-Hartman
parent fb7aa03db6
commit d8c1f929aa
4 changed files with 6 additions and 8 deletions
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4
drivers/tty/n_tty.c
View file

@ -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 @@ do_it_again:
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;
}

1
drivers/tty/tty_io.c
View file

@ -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);

8
drivers/tty/tty_ioctl.c
View file

@ -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;
}

1
include/linux/tty.h
View file

@ -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 */