diff options
| author | Peter Hurley <peter@hurleysoftware.com> | 2014-09-10 15:06:31 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-09-23 21:19:35 -0700 |
| commit | f9e053dcfc02b0ad29daec8524fb1afe09774976 (patch) | |
| tree | 2d930c2d89b011b40c03eeb13ee6f431cb602d3f /drivers/tty | |
| parent | d7a855bd6ab25d10d5e3b6aeb53d9c57fa17b808 (diff) | |
tty: Serialize tty flow control changes with flow_lock
Without serialization, the flow control state can become inverted
wrt. the actual hardware state. For example,
CPU 0 | CPU 1
stop_tty() |
lock ctrl_lock |
tty->stopped = 1 |
unlock ctrl_lock |
| start_tty()
| lock ctrl_lock
| tty->stopped = 0
| unlock ctrl_lock
| driver->start()
driver->stop() |
In this case, the flow control state now indicates the tty has
been started, but the actual hardware state has actually been stopped.
Introduce tty->flow_lock spinlock to serialize tty flow control changes.
Split out unlocked __start_tty()/__stop_tty() flavors for use by
ioctl(TCXONC) in follow-on patch.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/tty_io.c | 39 |
1 files changed, 28 insertions, 11 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index d4eb2a8b7047..b8ddfef6b5d8 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -919,18 +919,18 @@ void no_tty(void) * but not always. * * Locking: - * Uses the tty control lock internally + * ctrl_lock + * flow_lock */ -void stop_tty(struct tty_struct *tty) +void __stop_tty(struct tty_struct *tty) { unsigned long flags; - spin_lock_irqsave(&tty->ctrl_lock, flags); - if (tty->stopped) { - spin_unlock_irqrestore(&tty->ctrl_lock, flags); + + if (tty->stopped) return; - } tty->stopped = 1; + spin_lock_irqsave(&tty->ctrl_lock, flags); if (tty->link && tty->link->packet) { tty->ctrl_status &= ~TIOCPKT_START; tty->ctrl_status |= TIOCPKT_STOP; @@ -941,6 +941,14 @@ void stop_tty(struct tty_struct *tty) (tty->ops->stop)(tty); } +void stop_tty(struct tty_struct *tty) +{ + unsigned long flags; + + spin_lock_irqsave(&tty->flow_lock, flags); + __stop_tty(tty); + spin_unlock_irqrestore(&tty->flow_lock, flags); +} EXPORT_SYMBOL(stop_tty); /** @@ -954,17 +962,17 @@ EXPORT_SYMBOL(stop_tty); * * Locking: * ctrl_lock + * flow_lock */ -void start_tty(struct tty_struct *tty) +void __start_tty(struct tty_struct *tty) { unsigned long flags; - spin_lock_irqsave(&tty->ctrl_lock, flags); - if (!tty->stopped || tty->flow_stopped) { - spin_unlock_irqrestore(&tty->ctrl_lock, flags); + + if (!tty->stopped || tty->flow_stopped) return; - } tty->stopped = 0; + spin_lock_irqsave(&tty->ctrl_lock, flags); if (tty->link && tty->link->packet) { tty->ctrl_status &= ~TIOCPKT_STOP; tty->ctrl_status |= TIOCPKT_START; @@ -977,6 +985,14 @@ void start_tty(struct tty_struct *tty) tty_wakeup(tty); } +void start_tty(struct tty_struct *tty) +{ + unsigned long flags; + + spin_lock_irqsave(&tty->flow_lock, flags); + __start_tty(tty); + spin_unlock_irqrestore(&tty->flow_lock, flags); +} EXPORT_SYMBOL(start_tty); /* We limit tty time update visibility to every 8 seconds or so. */ @@ -3019,6 +3035,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) INIT_WORK(&tty->hangup_work, do_tty_hangup); mutex_init(&tty->atomic_write_lock); spin_lock_init(&tty->ctrl_lock); + spin_lock_init(&tty->flow_lock); INIT_LIST_HEAD(&tty->tty_files); INIT_WORK(&tty->SAK_work, do_SAK_work); |