From 0733db91d06a555b3f85f0b4c958c8949ed22e1d Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Mon, 16 Jun 2014 09:16:59 -0400 Subject: [PATCH] tty: Document locking for tty_port_close{,start,end}() 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 Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_port.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index 3f746c8eb0dd..bcc15f75646c 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -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) { -- 2.34.1