Commit ddc7b758 authored Jun 16, 2014 by Peter Hurley Committed by Greg Kroah-Hartman Jul 10, 2014

tty: Move tty->closing from port lock critical section



tty->closing informs the line discipline that the hardware will
be shutting down imminently, and to disable further input other
than soft flow control (but to still allow additional output).

However, the tty lock is the necessary lock for preventing
concurrent changes to tty->closing. As shown by the call-tree
audit [1] of functions that modify tty->closing, the tty lock
is already held for those functions.

[1]
Call-tree audit of functions that modify tty->closing
* does not include call tree to tty_port_close(), tty_port_close_start(),
  or tty_port_close_end() which is already documented in
  'tty: Document locking for tty_port_close{,start,end}' that shows
  callers to those 3 functions hold the tty lock

tty_release()
  tty->ops->close() --+
                      |
__tty_hangup()        |
  tty->ops->close() --+
                      |
        mp_close():drivers/staging/sb105x/sb_pci_mp.c
        dngc_tty_close():drivers/staging/dgnc/dgnc_tty.c
        dgap_tty_close():drivers/staging/dgap/dgap_tty.c
        dgrp_tty_close():drivers/staging/dgrp/dgrp_tty.c
        rp_close():drivers/tty/rocket.c
        hvsi_close():drivers/tty/hvc/hvsi.c
        rs_close():drivers/tty/serial/68328serial.c
        rs_close():drivers/tty/serial/crisv10.c
        uart_close():drivers/tty/serial/serial_core.c
        isdn_tty_close():drivers/isdn/i4l/isdn_tty.c
        tty3215_close():drivers/s390/char/con3215.c

tty_open()
  tty_ldisc_setup() ----+
                        |
__tty_hangup()          |
  tty_ldisc_hangup() ---+
                        |
tty_set_ldisc() --------+
  tty_ldisc_restore() --+
                        |
                        +- tty_ldisc_open()
                             ld->ops->open() --+
                                               |
                                               +- n_tty_open()

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 9c9928bd

drivers/tty/serial/serial_core.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1368,8 +1368,8 @@ static void uart_close(struct tty_struct tty, struct file filp)
		tty_ldisc_flush(tty);

		tty_port_tty_set(port, NULL);
		spin_lock_irqsave(&port->lock, flags);
		tty->closing = 0;
		spin_lock_irqsave(&port->lock, flags);

		if (port->blocked_open) {
		spin_unlock_irqrestore(&port->lock, flags);

drivers/tty/tty_port.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -497,9 +497,10 @@ int tty_port_close_start(struct tty_port *port,
		return 0;
		}
		set_bit(ASYNCB_CLOSING, &port->flags);
		tty->closing = 1;
		spin_unlock_irqrestore(&port->lock, flags);

		tty->closing = 1;

		if (test_bit(ASYNCB_INITIALIZED, &port->flags)) {
		/* Don't block on a stalled port, just pull the chain */
		if (tty->flow_stopped)
		@@ -522,9 +523,10 @@ void tty_port_close_end(struct tty_port port, struct tty_struct tty)
		{
		unsigned long flags;

		spin_lock_irqsave(&port->lock, flags);
		tty->closing = 0;

		spin_lock_irqsave(&port->lock, flags);

		if (port->blocked_open) {
		spin_unlock_irqrestore(&port->lock, flags);
		if (port->close_delay) {

Admin message