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Date: Mon, 16 Jun 2014 09:16:59 -0400
From: Peter Hurley <peter@...leysoftware.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH tty-next 02/22] 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 <peter@...leysoftware.com>
---
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 3f746c8..bcc15f7 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)
{
--
2.0.0
--
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