The low-level uart driver may modify termios settings to override settings that are not compatible with the uart, such as CRTSCTS. Thus, callers of the low-level uart driver's set_termios() method must hold termios_rwsem write lock to prevent concurrent access to termios, in case such override occurs.
The termios_rwsem lock requirement does not extend to console setup (ie., uart_set_options), as console setup cannot race with tty operations. Nor does this lock requirement extend to functions which cannot be concurrent with tty ioctls (ie., uart_port_startup() and uart_resume_port()). Further, always claim the port mutex to protect hardware re-reprogramming in the set_termios() uart driver method. Note this is unnecessary for console initialization in uart_set_options() which cannot be concurrent with other uart operations. Signed-off-by: Peter Hurley <[email protected]> --- Documentation/serial/driver | 6 ++++-- drivers/tty/serial/serial_core.c | 8 +++++++- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/Documentation/serial/driver b/Documentation/serial/driver index c3a7689..b1a22d4 100644 --- a/Documentation/serial/driver +++ b/Documentation/serial/driver @@ -59,7 +59,9 @@ The core driver uses the info->tmpbuf_sem lock to prevent multi-threaded access to the info->tmpbuf bouncebuffer used for port writes. The port_sem semaphore is used to protect against ports being added/ -removed or reconfigured at inappropriate times. +removed or reconfigured at inappropriate times. Since v2.6.27, this +semaphore has been the 'mutex' member of the tty_port struct, and +commonly referred to as the port mutex (or port->mutex). uart_ops @@ -246,7 +248,7 @@ hardware. Other flags may be used (eg, xon/xoff characters) if your hardware supports hardware "soft" flow control. - Locking: none. + Locking: caller holds port->mutex Interrupts: caller dependent. This call must not sleep diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 15212d7..5ed5a46 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -427,7 +427,7 @@ uart_get_divisor(struct uart_port *port, unsigned int baud) EXPORT_SYMBOL(uart_get_divisor); -/* FIXME: Consistent locking policy */ +/* Caller holds port mutex */ static void uart_change_speed(struct tty_struct *tty, struct uart_state *state, struct ktermios *old_termios) { @@ -1162,11 +1162,15 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd, break; case TIOCSSERIAL: + down_write(&tty->termios_rwsem); ret = uart_set_info_user(tty, state, uarg); + up_write(&tty->termios_rwsem); break; case TIOCSERCONFIG: + down_write(&tty->termios_rwsem); ret = uart_do_autoconfig(tty, state); + up_write(&tty->termios_rwsem); break; case TIOCSERGWILD: /* obsolete */ @@ -1268,7 +1272,9 @@ static void uart_set_termios(struct tty_struct *tty, return; } + mutex_lock(&state->port.mutex); uart_change_speed(tty, state, old_termios); + mutex_unlock(&state->port.mutex); /* reload cflag from termios; port driver may have overriden flags */ cflag = tty->termios.c_cflag; -- 2.0.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
