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

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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>
This commit is contained in:
Peter Hurley 2014-06-16 09:17:03 -04:00 committed by Greg Kroah-Hartman
parent 9c9928bded
commit ddc7b758a6
2 changed files with 5 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/tty/serial/serial_core.c
View File

@ -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);

6
drivers/tty/tty_port.c
View File

@ -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) {