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authorPeter Hurley <peter@hurleysoftware.com>2014-06-16 17:17:00 +0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-07-11 03:05:19 +0400
commitaddd4672bb442b23d16f91c5bae866ba1f9ffd4c (patch)
treefb21b770969a5d9aab7e1f85af837ee9c6a4a53b
parent0733db91d06a555b3f85f0b4c958c8949ed22e1d (diff)
downloadlinux-addd4672bb442b23d16f91c5bae866ba1f9ffd4c.tar.xz
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 <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/tty_port.c8
1 files changed, 8 insertions, 0 deletions
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)
{