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Commit 7c8ab967 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
Browse files

serial: Fix locking for uart driver set_termios() method 



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: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2e758910

Documentation/serial/driver

+4 −2
Original line number Diff line number Diff line
@@ -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
@@ -248,7 +250,7 @@ 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

drivers/tty/serial/serial_core.c

+7 −1
Original line number Diff line number Diff line
@@ -436,7 +436,7 @@ 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)

{
@@ -1173,11 +1173,15 @@ 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 */
@@ -1278,7 +1282,9 @@ 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;