From b68f2fb9e73f46037fbeca5fbd4ae8a7ddd8ef6b Mon Sep 17 00:00:00 2001 From: Alan Cox Date: Mon, 27 Jul 2009 10:58:08 +0100 Subject: [PATCH] tty: Fix a USB serial crash/scribble The port lock is used to protect the port state. However the port structure is freed on a hangup, then the lock taken on a close. The right fix is to drop the port on tty->shutdown() but we can't yet do that due to sleep v non-sleeping rules. Instead do the next best thing and fix it up when we are not in -rc season. Reported-by: Daniel Mack Signed-off-by: Alan Cox Tested-by: Daniel Mack Signed-off-by: Linus Torvalds --- drivers/usb/serial/usb-serial.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c index bd7581b3a48a..3c8923f62ed1 100644 --- a/drivers/usb/serial/usb-serial.c +++ b/drivers/usb/serial/usb-serial.c @@ -340,6 +340,22 @@ static void serial_close(struct tty_struct *tty, struct file *filp) dbg("%s - port %d", __func__, port->number); + /* FIXME: + This leaves a very narrow race. Really we should do the + serial_do_free() on tty->shutdown(), but tty->shutdown can + be called from IRQ context and serial_do_free can sleep. + + The right fix is probably to make the tty free (which is rare) + and thus tty->shutdown() occur via a work queue and simplify all + the drivers that use it. + */ + if (tty_hung_up_p(filp)) { + /* serial_hangup already called serial_down at this point. + Another user may have already reopened the port but + serial_do_free is refcounted */ + serial_do_free(port); + return; + } if (tty_port_close_start(&port->port, tty, filp) == 0) return; @@ -355,7 +371,8 @@ static void serial_hangup(struct tty_struct *tty) struct usb_serial_port *port = tty->driver_data; serial_do_down(port); tty_port_hangup(&port->port); - serial_do_free(port); + /* We must not free port yet - the USB serial layer depends on it's + continued existence */ } static int serial_write(struct tty_struct *tty, const unsigned char *buf, -- 2.20.1