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tty: Document locking for tty_port_close{,start,end}()

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The tty lock is held when the tty driver's .close method is called
(from the two lone call-sites of tty_release() and __tty_hangup()).
The call-tree audit[1] of tty_port_close(), tty_port_close_start,
and tty_port_close_end() is a closed graph of the callers of these
3 functions; ie., all callers originate from only tty_release()
or __tty_hangup().

Of these callers, none drop the tty lock.

Also, document tty_port_close_start() may drop and reacquire the
tty lock in tty_wait_until_sent_from_close(), which means the tty
or tty_port may have changed state (but not reopened or hung up).

[1]
Call-tree audit of tty_port_close, tty_port_close_start, and tty_port_close_end()

tty_release()
  tty->ops->close() --+
                      |
__tty_hangup()        |
  tty->ops->close() --+
                      |
                      +- rp_close():drivers/tty/rocket.c -------------------+
                      +- uart_close():drivers/tty/serial/serial_core.c -----+
                      |                                                     +- tty_port_close_start()
                      |
                      |
                      +- close():drivers/tty/synclinkmp.c ------------------+
                      +- rs_close():drivers/tty/amiserial.c ----------------+
                      +- gsmtty_close():drivers/tty/n_gsm.c ----------------+
                      +- mxser_close():drivers/tty/mxser.c -----------------+
                      +- close():drivers/tty/synclink_gt.c -----------------+
                      +- mgsl_close():drivers/tty/synclink.c ---------------+
                      +- isdn_tty_close():drivers/isdn/i4l/isdn_tty.c ------+
                      +- mgslpc_close():drivers/char/pcmcia/synclink_cs.c --+
                      +- ircomm_tty_close():net/irda/ircomm/ircomm_tty.c ---+
                      |                                                     |
        rs_close():arch/ia64/hp/sim/simserial.c                             |
       *line_close():arch/um/drivers/line.c                                 |
        gdm_tty_close():drivers/staging/gdm724x/gdm_tty.c
        fwtty_close():drivers/staging/fwserial/fwserial.c
        acm_tty_close():drivers/usb/class/cdc-acm.c
        serial_close():drivers/usb/serial/usb-serial.c
        pti_tty_driver_close():drivers/misc/pti.c
        ipoctal_close():drivers/ipack/devices/ipoctal.c
        cy_close():drivers/tty/cyclades.c
        isicom_close():drivers/tty/isicom.c
        dashtty_close():drivers/tty/metag_da.c
        moxa_close():drivers/tty/moxa.c
        goldfish_tty_close():drivers/tty/goldfish.c
        ehv_bc_tty_close():drivers/tty/ehv_bytechan.c
        kgdb_nmi_tty_close():drivers/tty/serial/kgdb_nmi.c
        ifx_spi_close():drivers/tty/serial/ifx6x60.c
        smd_tty_close():drivers/tty/serial/msm_smd_tty.c
        ntty_close():drivers/tty/nozomi.c
        capinc_tty_close():drivers/isdn/capi/capi.c
        tpk_close():drivers/char/ttyprintk.c
        sdio_uart_close():drivers/mmc/card/sdio_uart.c                      |
        rfcomm_tty_close():net/bluetooth/rfcomm/tty.c                       |
                      |                                                     |
                      +- tty_port_close():drivers/tty/tty_port.c -----------+
                                                                            |
                                                                            +- tty_port_close_start()
                                                                            +- tty_port_close_end()

* line_close() is the .close method for 2 um drivers,
  declared in ./arch/um/drivers/stdio_console.c and
  in ./arch/um/drivers/ssl.c, and not called directly

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 09:16:59 -04:00 committed by Greg Kroah-Hartman
parent ed617e4423
commit 0733db91d0
1 changed files with 14 additions and 0 deletions
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14
drivers/tty/tty_port.c
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@ -458,6 +458,10 @@ static void tty_port_drain_delay(struct tty_port *port, struct tty_struct *tty)
schedule_timeout_interruptible(timeout);
}
/* Caller holds tty lock.
* NB: may drop and reacquire tty lock (in tty_wait_until_sent_from_close())
* so tty and tty port may have changed state (but not hung up or reopened).
*/
int tty_port_close_start(struct tty_port *port,
struct tty_struct *tty, struct file *filp)
{
@ -506,6 +510,7 @@ int tty_port_close_start(struct tty_port *port,
}
EXPORT_SYMBOL(tty_port_close_start);
/* Caller holds tty lock */
void tty_port_close_end(struct tty_port *port, struct tty_struct *tty)
{
unsigned long flags;
@ -528,6 +533,15 @@ void tty_port_close_end(struct tty_port *port, struct tty_struct *tty)
}
EXPORT_SYMBOL(tty_port_close_end);
/**
* tty_port_close
*
* Caller holds tty lock
*
* NB: may drop and reacquire tty lock (in tty_port_close_start()->
* tty_wait_until_sent_from_close()) so tty and tty_port may have changed
* state (but not hung up or reopened).
*/
void tty_port_close(struct tty_port *port, struct tty_struct *tty,
struct file *filp)
{