From addd4672bb442b23d16f91c5bae866ba1f9ffd4c Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Mon, 16 Jun 2014 09:17:00 -0400 Subject: [PATCH] tty: Document locking for tty_port_open() The tty lock is held when the tty driver's open method is called (from the lone call-site, tty_open()). The call-tree audit [1] of tty_port_open() is a closed graph of the callers of tty_port_open(); ie., all callers originate from only tty_open(). Of these callers, none drop the tty lock. Also, document that tty_port_block_til_ready() may drop and reacquire the tty lock when blocking, which means the tty or tty_port may have changed state. [1] Call-tree audit of tty_port_open() tty_open() tty->ops->open() --+ | rs_open():arch/ia64/hp/sim/simserial.c *line_open():arch/um/drivers/line.c gdm_tty_open():drivers/staging/gdm724x/gdm_tty.c fwtty_open():drivers/staging/fwserial/fwserial.c acm_tty_open():drivers/usb/class/cdc-acm.c serial_open():drivers/usb/serial/usb-serial.c pti_tty_driver_open():drivers/misc/pti.c ipoctal_open():drivers/ipack/devices/ipoctal.c isicom_open():drivers/tty/isicom.c dashtty_open():drivers/tty/metag_da.c goldfish_tty_open():drivers/tty/goldfish.c ehv_bc_tty_open():drivers/tty/ehv_bytechan.c mxser_open():drivers/tty/mxser.c kgdb_nmi_tty_open():drivers/tty/serial/kgdb_nmi.c ifx_spi_open():drivers/tty/serial/ifx6x60.c smd_tty_open():drivers/tty/serial/msm_smd_tty.c ntty_open():drivers/tty/nozomi.c capinc_tty_open():drivers/isdn/capi/capi.c tpk_open():drivers/char/ttyprintk.c sdio_uart_open():drivers/mmc/card/sdio_uart.c rfcomm_tty_open():net/bluetooth/rfcomm/tty.c | +- tty_port_open() * line_open() is the .open 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 | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index bcc15f75646c..f4698696abae 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -572,6 +572,14 @@ int tty_port_install(struct tty_port *port, struct tty_driver *driver, } EXPORT_SYMBOL_GPL(tty_port_install); +/** + * tty_port_open + * + * Caller holds tty lock. + * + * NB: may drop and reacquire tty lock (in tty_port_block_til_ready()) so + * tty and tty_port may have changed state (eg., may be hung up now) + */ int tty_port_open(struct tty_port *port, struct tty_struct *tty, struct file *filp) { -- 2.39.2